Optical signal reception device and method of controlling optical signal reception

ABSTRACT

An optical signal reception device that receives and demodulates an optical signal modulated by DQPSK and performs logical inversion and other controls to transit to the object reception state. The signal reception device includes a front end including a delay interferometer and an opto-electric conversion element that receive the DQPSK optical signal and convert it into an in-phase signal and a quadrature-phase signal, a clock regenerator that regenerates a clock signal based on the in-phase signal and the quadrature-phase signal, a multiplexer that multiplexes the in-phase signal and the quadrature-phase signal, a reception frame processing unit that detects frame synchronization based on the signal multiplexed by the multiplexer and de-maps the received frames, and a controller that, based on out-of-frame-synchronization information (LOF/OOF) from the reception frame processing unit, performs logical inversion control in the clock regenerator, multiplexing timing control in the multiplexer, and controls the delay interferometer in the front end so as to transit to the object reception state.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional and claims priority of U.S. Ser. No.11/510,729, filed Aug. 28, 2006, now allowed, which is acontinuation-in-part of U.S. Ser. No. 11/282,886, filed Nov. 21, 2005,now abandoned. This application is also based upon and claims thepriority of Japanese application nos. 2005-054371, filed Feb. 28, 2005,2005-206467, filed Jul. 15, 2005 and 2006-116291, filed Apr. 20, 2006,the contents of the foregoing applications all being incorporated hereinby reference.

BACKGROUND

1. Field

The present invention relates to an optical signal reception device forreceiving and demodulating optical signals modulated by a DifferentialQuadrature Phase Shift Keying (DQPSK) modulation scheme or aDifferential Phase Shift Keying (DPSK) modulation scheme in order toachieve high speed data transmission, and a method of controllingreception of optical signals.

2. Description of the Related Art

In digital communication systems, typically the Internet (IP: InternetProtocol), in order to meet rapidly increasing needs of digitalcommunication, an optical communication scheme employing IM-DQPSK(Intensity Modulation Differential Quadrature Phase Shift Keying)modulation scheme is being studied to improve utilization offrequencies.

For details of IM-DQPSK, reference can be made to P. S. Cho, V. S.Grigoryan, Y. A. Godin, A. Salamon, and Y. Achiam, “Transmission of 25Gbps RZ-DQPSK signals with 25-GHz channel spacing over 1000 km of SMF-28fiber”, IEEE Photonic Technical Letter, Vol. 15, pp. 473-475, March 2003(hereinafter, referred to as “reference 1”), and H. Kim, and R-J.Essiambre, “Transmission of 8×20 Gbps DQPSK signals with 25-GHz channelspacing over a 310-km SMF with 0.8-b/s/Hz spectral efficiency”, IEEEPhotonic Technical Letter, Vol. 15, pp. 769-771, May, 2003 (hereinafter,referred to as “reference 2”).

FIG. 38 is a block diagram illustrating an optical transponder (anoptical sender and an optical receiver) employing the above IM-DQPSKmodulation scheme.

The optical transponder illustrated in FIG. 38 includes a framer LSI100, an optical receiver (40 G OR) 101, a serializer (SER) 102, ade-multiplexer (DEMUX) 103, a DQPSK precoder 104, a DQPSK modulator (40G OS DQPSK) 105, a DQPSK optical sender (40 G OS) 106, a de-serializer(DES) 107, a multiplexer (MUX) 108, and a DQPSK demodulator (40 G ORDQPSK) 109.

The DQPSK modulator 105, as schematically exemplified in an expandedportion thereabove in FIG. 38, includes a DFB-LD (Distributed FeedbackLaser), a phase modulation section 112, an intensity modulator 113, anda driver. The phase modulation section 112 includes phase modulators114, 115 and a π/2 phase shifter.

The DQPSK demodulator 109, as schematically exemplified in an expandedportion therebelow in FIG. 38, includes a π/4 delay interferometer 116,a −π/4 delay interferometer 117, photo-diodes (PDs) acting asopto-electric conversion elements, and amplifiers (amp). It should benoted that the configuration of the DQPSK demodulator 109 in FIG. 38 asdescribed above illustrates a state in which the optical transmissiondirection is reversed.

In FIG. 38, it is illustrated that the transponder converts data signalstransmitted at a bit rate of 40 Gbps into optical signals, modulates theoptical signals by the DQPSK modulation scheme, and transmits thesignals.

As illustrated in FIG. 38, the optical receiver 101 receives the opticalsignals transmitted at a bit rate of 40 Gbps from a client (user) side,converts the optical signals into electrical signals, and outputs 16parallel signals each at a bit rate of 2.5 Gbps (=40 Gbps/16) to theframer LSI 100.

The framer LSI 100 transforms each of the 16 parallel signals from theoptical receiver 101 into multiple frames, and performs mapping andde-mapping on each frame by means of, for example, SONET (SynchronousOptical Network), SDH (Synchronous Digital Hierarchy), or OTN (OpticalTransport Network). In this figure, it is assumed that the framer LSI100 is the one for OTN.

After the frame processing, the framer LSI 100 outputs 16 parallelsignals each at 2.7 Gbps.

A serializer 102 converts the 16 parallel signals at a bit rate of 2.7Gbps from the framer LSI 100 into a serial data signal at 43 Gbps.

The de-multiplexer (DEMUX) 103 receives the serial data signal at 43Gbps and a clock signal (CLK) at 21.5 GHz, de-multiplexes the signalsfrom the serializer 102 at a de-multiplexing ratio of 1 to 2, andgenerates two parallel signals I_(k) and Q_(k) each at 21.5 Gbps.

The signals I_(k) and Q_(k) output from the de-multiplexer (DEMUX) 103are input to the DQPSK precoder 104. The DQPSK precoder 104 converts thesignals I_(k) and Q_(k) into signals ρ_(k) and η_(k), and inputs theobtained signals ρ_(k) and η_(k) to the DQPSK demodulator 105.

The DQPSK precoder 104 converts the input in-phase signals I_(k) andquadrature-phase signals Q_(k) into signals ρ_(k) and η_(k) according tothe following logical relations.

ρ_(k) =Q _(k)ρ_(k−1)η_(k−1) +I _(k)ρ_(k−1) η_(k−1) + I _(k)ρ_(k−1)η_(k−1)+ Q _(k)ρ_(k−1)η_(k−1)

η_(k) =I _(k)ρ_(k−1)η_(k−1)+ Q _(k) ρ_(k−1) η_(k−1) +Q _(k) ρ_(k−1)η_(k−1)+ I _(k)ρ_(k−1)η_(k−1)

FIG. 39 is a circuit diagram illustrating an example of a configurationof the DQPSK precoder 104.

As illustrated in FIG. 39, the DQPSK precoder 104 may be a logic gatecircuit constructed by combining logical OR circuits, logical ANDcircuits, and inhibit circuits or other kinds of logic circuits. In FIG.39, “D” indicates a one-bit delay circuit.

The signals ρ_(k) and η_(k) (at 21.5 Gbps) encoded by the DQPSK precoder104 are input to the DQPSK modulator 105. The DQPSK modulator 105converts the signals ρ_(k) and η_(k) into DQPSK optical signals andsends the optical signals to the network side.

The DQPSK modulator 105 splits a light beam emitted from the DFB-LD 111into two beams, outputs one of the two split light beams into the phasemodulator 114, and shifts the phase of the other split light beam by π/2and outputs the phase-shifted light beam into the phase modulator 115.The phase modulators 114 and 115 perform phase modulation on therespective input light beams according to the respective signals ρ_(k)and η_(k) from the precoder 104 at 21.5 Gbps. The output light beamsfrom the phase modulators 114 and 115 are combined and are input to theintensity modulator 113. The intensity modulator 113 performs intensitymodulation on the input optical signals according to the clock signal(clock) at 21.5 GHz, and generates and transmits IM-DQPSK opticalsignals at 43 Gbps.

For example, each of the phase modulators 114 and 115, and the intensitymodulator 113 of the DQPSK modulator 105 may be structured by aMach-Zehnder interferometer formed by elements having theelectro-optical effect, such as LiNbO₃.

The DQPSK demodulator 109 receives the DQPSK optical signals from thenetwork side, splits the optical signals into two portions, outputs oneportion into the π/4 delay interferometer 116, delays the phase of theother portion by −π/4, and outputs the resulting optical signals intothe −π/4 delay interferometer 117.

Each of the delay interferometers 116 and 117, for example, generates apath length difference between two path lengths each being constitutedby a light guide, and generates a time delay τ corresponding to onesymbol of the modulated optical signal.

The delay interferometer 116 has a π/4 phase shifter in an arm thereoffor generating a π/4 phase shift, and the delay interferometer 117 has a−π/4 phase shifter in an arm thereof for generating a −π/4 phase shift.

Optical signals from arms of the delay interferometers 116 and 117 entera pair of photo detectors (PD) as light receiving elements via couplersat the output stages of the delay interferometers 116 and 117, and afteropto-electric conversion, an in-phase signal I_(k) is output from theside of the delay interferometer 116, and an quadrature-phase signalQ_(k) is output from the side of the delay interferometer 117.

The multiplexer (MUX) 108 multiplexes the data signals I_(k) and Q_(k)from the DQPSK optical demodulator 109 at 21.5 Gbps to convert the datasignals I_(k) and Q_(k) into a serial data signal at about 43 Gbps, andoutputs the serial data signal at about 43 Gbps and the clock signal(clock) at 21.5 GHz to the de-serializer (DES) 107 in parallel.

The de-serializer 107 converts the serial data signal at about 43 Gbpsinto 16 parallel signals each at about 2.7 Gbps, and outputs theresulting signals into the framer LSI 100.

The framer LSI 100 de-maps the SONET, SDH or OTN frames, obtains 16parallel signals each at about 2.5 Gbps, and outputs the 16 parallelsignals to the optical sender 106.

The optical sender 106 converts the 16 parallel signals into a serialoptical signal, and sends the optical signal at about 43 Gbps to theclient side.

In addition, it is proposed to use Mach-Zehnder type delayinterferometers in DMPSK (Differential Multiple Phase Shift Keying)optical signal modulation and demodulation unit with M=2^(n). Forexample, such an optical communication system is disclosed inInternational Application's Japanese Publication No. 2004-516743, inwhich the DMPSK modulation scheme becomes the same as the above DQPSKmodulation scheme when n=2.

In addition, for example, an optical communication system is disclosedin International Application's Japanese Publication No. 2004-533163, inwhich a phase-modulated optical signal is intensity-modulated by a clocksignal and is then transmitted; on a receiver end, the clock signal isrecovered based on the intensity-modulated component.

FIG. 40 is a block diagram illustrating a principal portion of anoptical signal receiver used in an optical communication system fortransmitting the DQPSK optical signals.

Illustrated in FIG. 40 are a front end 121 (40 G DQPSK OR), a clock anddata recovery (20 G CDR A) 123, a clock and data recovery (20 G CDR B)124, a multiplexer (MUX) 126, a de-serializer (DES) 128, and a framerLSI 129 acting as a frame processing unit.

In FIG. 40, the direction of the signal flow is opposite to the path ofsignal reception processing in FIG. 38, but the functions of processingare the same.

Specifically, the front end 121 corresponds to the DQPSK demodulator 109in FIG. 38.

The multiplexer 126 multiplexes the signals output from each of theclock and data recovery 123 and the clock and data recovery 124 at amultiplexing ratio of 2:1.

The de-serializer (DES) 128 converts the input signals into 16 parallelsignals each at 2.7 Gbps.

The framer LSI 129 receives 16 parallel signals each at 2.7 Gbps, andhas the same de-mapping functions as the framer 100 in FIG. 38.

The in-phase signal component I_(k) and the quadrature-phase signalcomponent Q_(k) are output from a port A and a port B of the front end121. However, when DQPSK optical signals are transmitted through anoptical transmission path, waveforms of the optical signals may bedegraded because of influences of wavelength dispersion and thenon-linear effect of the optical fiber in use. In addition, because thetwo interferometers of the front end 121 are independent from eachother, if the optimum operating points of the two interferometers changewith age or due to temperature changes, probably, the signal I_(k) andthe signal Q_(k) satisfying desired logical relations cannot beobtained.

FIG. 41 is a block diagram illustrating principal portions of an opticalsignal receiver side and an optical signal transmitter side of theoptical transponder as shown in FIG. 38.

The structure shown in FIG. 41 includes a transmission processing unit421 (indicated as “OTN LSI” in FIG. 41), an optical modulationprocessing unit 422 (indicated as “43 G NB Mod (Tx side)”), an opticalsignal reception processing unit 423 (indicated as “43 G NB Mod (Rxside)”), and a reception processing unit 424 (indicated as “OTN LSI”).

In FIG. 41, an SFI-5 interface is a parallel signal interface forconnecting the transmission processing unit 421 and the opticalmodulation processing unit 422, and for connecting the optical signalreception processing unit 423 and the reception processing unit 424; theSFI-5 interface is in compliance with a 40 Gbps Serdes Framer Interfacestandard established by OIF-SFI5-01.02 of OIF (Optical Interface Forum).

It should be noted that the parallel signal interface for connecting thetransmission processing unit 421 and the optical modulation processingunit 422, and for connecting the optical signal reception processingunit 423 and the reception processing unit 424 is not limited to theSFI-5 interface, but can be other similar signal interfaces.

The transmission processing unit 421 includes a framer and others, andthe optical modulation processing unit 422 includes a serializer (SER),a de-multiplexer (1:2DEMUX), a driver which receives data η_(k), andρ_(k) for controlling a phase modulator, a DFB-LD (Distributed FeedbackSemiconductor Laser), and an intensity modulator. RZ-DQPSK opticalsignals output from the intensity modulator are transmitted as data attime k, k+1, k+2, . . . along the time axis, and are indicated as{I_(k), Q_(k)}, {I_(k+1), Q_(k+1)}, . . . .

The optical signal reception processing unit 423 includes a π/4 delayinterferometer, a −π/4 delay interferometer, photo-diodes (PDs) actingas opto-electric conversion elements, amplifiers (amp), a multiplexingprocessing unit CDR+2:1MUX for reproducing clocks and data and formultiplexing, and a de-serializer (DES), which corresponds to thestructure in FIG. 38 including the π/4 delay interferometer 116, the−π/4 delay interferometer 117, the photo-diodes (PDs), the amplifiers(amp), the multiplexer (MUX) 108, and the de-serializer (DES) 107.

Each of the multiplexing processing unit CDR+2:1MUX and thede-serializer (DES) is an integrated circuit.

The reception processing unit 424 corresponds to the framer 100 and theDQPSK optical sender 106 in FIG. 38.

In the optical signal reception processing unit 423, signals A_(k),A_(k+1), . . . obtained by opto-electric conversion from the π/4 delayinterferometer, and signals B_(k), B_(k+1), . . . obtained byopto-electric conversion from the −π/4 delay interferometer aremultiplexed by the multiplexing processing unit CDR+2:1MUX, resulting insignals A_(k), B_(k), A_(k+1), B_(k+1), . . . , and the signals A_(k),B_(k), A_(k+1), B_(k+1), . . . are transmitted to the de-serializer(DES); the de-serializer (DES) converts the signals A_(k), B_(k),A_(k+1), B_(k+1), . . . into 16 parallel signals, and transmits the 16parallel signals to the reception processing unit 424 including a framervia the SFI-5 interface. Depending on the timing of the serial-parallelconversion, the order of the 16 parallel signals may be determinedaccording to a combination of a case 1 and a case 2 as shown in FIG. 41,or a combination of a case 3 and a case 4 as shown in FIG. 41.

FIG. 42A through FIG. 42C are tables illustrating reception states inportions (a), (b), and (c) in FIG. 41.

FIG. 42A illustrates reception states of the optical signal receptionprocessing unit 423 with A channel (Ach) signals and B channel (Bch)signals under various conditions.

In the table in FIG. 42A, for example, a double circle indicates anobject signal reception state, single circles indicate that either the Achannel signal or the B channel signal or both of them are in a logicalinversion state relative to the object signal reception state, trianglesindicate a state generated by logical inversion and bit swap, a diamondindicates a state of bit swap, and crosses indicates states not allowingsignal reception such as synchronization pull-in state.

FIG. 42B and FIG. 42C illustrate reception states of a 16-parallelsignal interface between the de-serializer (DES) and the receptionprocessing unit 424.

Depending on the opto-electric conversion, clock/data regeneration(clock and data recovery) and multiplexing, and the order of signalsoutput from the de-serializer (DES), the reception state becomes one ofcase 1 through case 4, and the case 3 and case 4 correspond to one-bitshifted situation relative to the case 1 and case 2. For this reason,FIG. 42B represents reception states corresponding to the case 1 andcase 2, and FIG. 42C represents reception states corresponding to thecase 3 and case 4. In FIG. 42B and FIG. 42C, if double circles indicateobject signal reception states, as in FIG. 42A, reception statesrepresented by single circles, triangles, diamonds, and crosses occur.

As described above, in the object signal reception state, which isrepresented by the double circle, an optical signal reception processcan be performed normally, and frame synchronization can be established.However, in states other than the object signal reception state, theframe pull-in process cannot be performed, and hence, a normal signalreception process cannot be performed.

In addition, even when functions of components of the device arespecified in detail to designate the object signal reception state wheninitially starting the device, operation conditions of the componentsmay change with age or with temperature changes, and in this case, onehas to set the conditions of the components again.

SUMMARY

Accordingly, it is a general object of the present invention to solveone or more of the above problems of the related art.

A more specific object of the present invention is to provide an opticalsignal reception device that determines reception states of opticalsignals modulated by a DQPSK (Differential Quadrature Phase ShiftKeying) modulation scheme or a DPSK (Differential Phase Shift Keying)modulation scheme, performs control so that demodulated signals tosatisfy a predetermined logical relation, and allows signal receptionwith a normal logical relation being satisfied even when changes withage temperature changes occur.

Another specific object of the present invention is to an optical signalreception device and a method of controlling reception of opticalsignals capable of automatic control to maintain to an object signalreception state.

According to a first aspect of the present invention, there is provideda signal reception device for receiving and demodulating an opticalsignal modulated by a Differential Quadrature Phase Shift Keying (DQPSK)modulation scheme, said signal reception device comprising: a front endincluding two delay interferometers and opto-electric conversionelements that receives the DQPSK optical signal and converts the DQPSKoptical signal into an in-phase signal and a quadrature-phase signal; aclock and data recovery that regenerates a clock and data signal basedon the in-phase signal and the quadrature-phase signal; a multiplexerthat multiplexes the in-phase signal and the quadrature-phase signaloutput from the clock and data recovery; a reception frame processingunit that detects frame synchronization based on the signal multiplexedby the multiplexer; and a controller that, based on a detection resultfrom the reception frame processing unit indicating anout-of-frame-synchronization state, controls logical inversionoperations in the clock and data recovery, controls a multiplexingtiming in the multiplexer, and controls the delay interferometers in thefront end.

As an embodiment, the reception frame processing unit comprises: a frameprocessor that performs a frame synchronization pull-in operation and aframe de-mapping operation; a frame synchronization circuit including aplurality of frame synchronization units, each of said framesynchronization units receiving a synchronization bit string in themultiplexed signal and performing frame synchronization detectionscorresponding to respective combinations of plural of thesynchronization bit strings; and an identification section thatidentifies a signal reception state depending on which one of the framesynchronization units a detection signal is output from, and notifiesthe controller of information of the signal reception stateidentification.

As an embodiment, the reception frame processing unit comprises: a frameprocessor that performs a frame synchronization pull-in operation and aframe de-mapping operation; a frame synchronization circuit that detectsa synchronization bit string in the multiplexed signal obtained bymultiplexing the in-phase signal and the quadrature-phase signal in themultiplexer, and performs frame synchronization detections; a registerthat stores combinations of plural of the synchronization bit strings;and an identification section that, based on the synchronization bitstrings of the multiplexed signal and the synchronization bit stringsstored in the register, identifies a signal reception state, andnotifies the controller of the signal reception state.

As an embodiment, the controller, based on the signal reception stateidentification information, determines whether a detected signalreception state is an object state, whether the detected signalreception state is a state convertible to the object state by thelogical inversion control, or whether the detected signal receptionstate is a state convertible to the object state by the logicalinversion control and the multiplexing timing control; the controllerdoes not perform control operations when the detected signal receptionstate is the object state; the controller controls the clock and datarecovery to perform the logical inversion control when the detectedsignal reception state is a state convertible to the object state by thelogical inversion control; and the controller controls the clock anddata recovery to perform the logical inversion control and controls themultiplexer to perform the multiplexing timing control when the detectedsignal reception state is a state convertible to the object state by thelogical inversion control and the multiplexing timing control.

As an embodiment, the signal reception device further comprises anin-phase detector configured to detect whether a quadrature phaserelation holds based on exclusive OR logic between the in-phase signaland the quadrature-phase signal input to the multiplexer; wherein thecontroller shifts a phase of the delay interferometers by π/2 or −π/2based on detection results of the in-phase detector.

According to a second aspect of the present invention, there is provideda signal reception device for receiving and demodulating an opticalsignal modulated by a Differential Quadrature Phase Shift Keying (DQPSK)modulation scheme, said signal reception device comprising: a front endincluding a polarization controller that converts the DQPSK opticalsignal into a line-polarized optical signal, a delay interferometer thatreceives the line-polarized optical signal, a polarizing beam splitterthat splits optical signals output from the delay interferometer, and adifferential light receiver that has two light-receiving elements forconverting the optical signals split by the polarizing beam splitterinto an in-phase signal and a quadrature phase signal, respectively; aclock and data recovery that regenerates a clock and data signal basedon the in-phase signal and the quadrature-phase signal; a multiplexerthat multiplexes the in-phase signal and the quadrature-phase signaloutput from the clock and data recovery; a reception frame processingunit that detects frame synchronization and identifies a reception statebased on the signal multiplexed by the multiplexer, and de-maps receivedframes; and a controller that controls logical inversion operations inthe clock and data recovery, controls a multiplexing timing in themultiplexer, and controls the delay interferometers in the front endbased on a detection result indicating an out-of-frame-synchronizationstate and reception state identification information from the receptionframe processing unit.

According to a third aspect of the present invention, there is provideda signal reception device for receiving and demodulating an opticalsignal modulated by a Differential Quadrature Phase Shift Keying (DQPSK)modulation scheme, said signal reception device comprising: a front endincluding two delay interferometer and opto-electric conversion elementsthat receive the DQPSK optical signal and convert the DQPSK opticalsignal into an in-phase signal and a quadrature-phase signal; a clockand data recovery that regenerates a clock and data signal based on thein-phase signal and the quadrature-phase signal; a multiplexer thatmultiplexes the in-phase signal and the quadrature-phase signal outputfrom the clock and data recovery; a reception frame processing unit thatdetects frame synchronization based on the signal multiplexed by themultiplexer; a controller that controls the delay interferometers in thefront end; and an in-phase detector that detects whether a quadraturephase relation holds based on exclusive OR logic between the in-phasesignal and the quadrature-phase signal input to the multiplexer, whereinthe controller shifts a phase of the delay interferometers by π/2 or−π/2 based on detection results of the in-phase detector.

According to a fourth aspect of the present invention, there is provideda signal reception device that receives and demodulates an opticalsignal, which optical signal is modulated by a Differential QuadraturePhase Shift Keying (DQPSK) modulation scheme and has a modulatedintensity, said signal reception device comprising: an optical couplerthat splits the DQPSK modulated optical signal; a front end includingtwo delay interferometers and an opto-electric conversion elements thatreceives the split DQPSK modulated optical signal and converts the splitDQPSK modulated optical signal into an in-phase electric signal and aquadrature-phase electric signal; a clock recovery that receives thesplit DQPSK modulated optical signal, and regenerates a clock signalbased on an intensity-modulated component of the split DQPSK modulatedoptical signal; a multiplexer that multiplexes the in-phase signal andthe quadrature-phase signal output from the front end in accordance withthe clock signal from the clock recovery; a reception frame processingunit that detects frame synchronization based on the signal multiplexedby the multiplexer; and a controller that, based on aframe-synchronization detection result from the reception frameprocessing unit indicating whether an object reception state isdetected, controls a multiplexing timing in the multiplexer, andcontrols the delay interferometers in the front end.

As an embodiment, the reception frame processing unit comprises at leastone of a logic inversion circuit that performs logic inversion of inputdata according to a logic inversion control signal from the controller,and a neighboring bit exchanging circuit that exchanges neighboring bitsof the input data.

As an embodiment, according to a logic inversion control signal from thecontroller, the reception frame processing unit performs logic inversioncontrol on an in-phase signal component and a quadrature-phase signalcomponent output from the front end, independently.

According to a fifth aspect of the present invention, there is provideda signal reception device for receiving and demodulating an opticalsignal modulated by a Differential Phase Shift Keying (DPSK) modulationscheme, said signal reception device comprising: a front end including adelay interferometer and opto-electric conversion elements that receivesthe DPSK optical signal and converts the DPSK optical signal into anelectric signal; a clock and data recovery that regenerates a clock anddata signal based on an output signal from the front end; ade-serializer that receives the clock signal from the clock and datarecovery and data from the front end and converts the clock signal andthe data into parallel signals; a reception frame processing unit thatreceives the parallel data from the de-serializer and detects framesynchronization; and a controller that, based on a detection result fromthe reception frame processing unit indicating anout-of-frame-synchronization state, inputs a logical inversion controlsignal to the clock regenerator and inputs a control signal to the delayinterferometer in the front end.

According to a sixth aspect of the present invention, there is provideda signal reception device for receiving and demodulating an opticalsignal modulated by a Differential Phase Shift Keying (DPSK) modulationscheme, said signal reception device comprising: a front end including adelay interferometer and an opto-electric conversion element thatreceive the DPSK optical signal and convert the DPSK optical signal intoan electric signal; a clock and data recovery that regenerates a clocksignal based on an output signal from the front end; a de-serializerthat receives the clock signal from the clock and data recovery and datafrom the front end and converts the clock signal and the data intoparallel signals; a reception frame processing unit that includes aframe synchronization circuit and a logic inversion circuit; and acontroller that, based on a detection result from the reception frameprocessing unit indicating an out-of-frame-synchronization state, inputsa logical inversion control signal to the logical inversion circuit andinputs a control signal to the delay interferometer in the front end.

According to a seventh aspect of the present invention, there isprovided a signal reception device that receives and demodulates anoptical signal, which optical signal is modulated by a DifferentialPhase Shift Keying (DPSK) modulation scheme and has a modulatedintensity, said signal reception device comprising: an optical couplerthat splits the DPSK modulated optical signal; a front end including adelay interferometer and opto-electric conversion elements that receivethe split DPSK modulated optical signal and convert the split DPSKmodulated optical signal into an electric signal; a clock recovery thatregenerates a clock signal based on an intensity-modulated component ofthe split DPSK modulated optical signal; a de-serializer that convertsdata from the front end into parallel signals according to the clocksignal from the clock recovery; a reception frame processing unit thatdetects frame synchronization based on the parallel signals obtained inthe de-serializer; and a controller that, based on aframe-synchronization detection result from the reception frameprocessing unit indicating whether an object reception state isdetected, inputs a logical inversion control signal to the clockrecovery and controls the delay interferometer in the front end.

According to an eighth aspect of the present invention, there isprovided a signal reception device that receives and demodulates anoptical signal, which optical signal is modulated by a DifferentialPhase Shift Keying (DPSK) modulation scheme and has a modulatedintensity, said signal reception device comprising: an optical couplerthat splits the DPSK modulated optical signal; a front end including adelay interferometer and opto-electric conversion elements that receivethe split DPSK modulated optical signal and convert the split DPSKmodulated optical signal into an electric signal; a clock recovery thatregenerates a clock signal based on an intensity-modulated component ofthe split DPSK modulated optical signal; a de-serializer that convertsdata from the front end into parallel signals according to the clocksignal from the clock recovery; a reception frame processing unitincluding a logic inversion circuit that performs logic inversion of theparallel signals obtained in the de-serializer, and a framesynchronization circuit that performs frame synchronization detection;and a controller that, based on a frame-synchronization detection resultfrom the reception frame processing unit indicating whether an objectreception state is detected, inputs a logical inversion control signalto the logic inversion circuit of the reception frame processing unitand controls the delay interferometer in the front end.

According to a ninth aspect of the present invention, there is provideda signal reception device for receiving and demodulating an opticalsignal modulated by a Differential Quadrature Phase Shift Keying (DQPSK)modulation scheme, said signal reception device comprising: a receptiondemodulation unit that includes a plurality of delay interferometers anda plurality of opto-electric conversion elements for receiving the DQPSKoptical signal and converting the DQPSK optical signal into an in-phasesignal and a quadrature-phase signal; a multiplexer that multiplexes thein-phase signal and the quadrature-phase signal; a de-serializing unitthat converts the multiplexed signals from the multiplexer into parallelsignals; and a reception processing unit that receives the parallelsignals from the de-serializing unit, and performs frame processingincluding frame synchronization processing, wherein the receptionprocessing unit includes a frame synchronization circuit thatestablishes frame synchronization, a reception state identificationcircuit that identifies reception states based on the parallel signals,and a logic processing circuit that performs logic inversion, bit delay,and bit swap corresponding to a reception state other than an objectreception state identified by the reception state identificationcircuit, and corresponding to a reception state related to ade-serializing timing in the de-serializing unit.

As an embodiment, the logic processing circuit of the receptionprocessing unit includes: a logic inversion circuit that controls,corresponding to a reception state identified by the reception stateidentification circuit, whether to perform logic inversion on thereceived parallel signals from the de-serializing unit, a one-bit delaycircuit that has a selector and a delay circuit to control whether ornot to delay the received parallel signals by one bit, and a bit swapcircuit that has a switching circuit for exchanging bits betweenadjacent channels of the received parallel signals.

As an embodiment, the reception state identification circuit compares aparallel frame synchronization pattern received from the de-serializingunit to a reception-state-corresponding comparison pattern to identify areception state, and the reception processing unit further includes acontroller that controls at least one of the logic inversion circuit,the one-bit delay circuit, and the bit swap circuit in response toidentification results of a reception state other than the objectreception state given by the reception state identification circuit, andcontrols at least one of the logic inversion circuit, the one-bit delaycircuit, and the bit swap circuit in response to a reception staterelated to the de-serializing timing in the de-serializing unit when theframe synchronization is not established by the frame synchronizationcircuit.

As an embodiment, the reception demodulation unit includes a π/4 delayinterferometer and a −π/4 delay interferometer, the reception stateidentification circuit of the reception processing unit has fourreception-state-corresponding comparison patterns so as to maintain aphase difference of the π/4 delay interferometer and the −π/4 delayinterferometer to be π/2, said four reception-state-correspondingcomparison patterns including the object reception state, and thereception processing unit further includes a controller that controls atleast one of the logic inversion circuit, the one-bit delay circuit, andthe bit swap circuit according to a reception state identified bycomparing a parallel frame synchronization pattern received from thede-serializing unit to the four reception-state-corresponding comparisonpatterns, and controls at least one of the logic inversion circuit, theone-bit delay circuit, and the bit swap circuit in response to areception state related to the de-serializing timing in thede-serializing unit when the frame synchronization is not established bythe frame synchronization circuit.

According to a 10th aspect of the present invention, there is provided amethod of controlling signal reception for receiving and demodulating anoptical signal modulated by a Differential Quadrature Phase Shift Keying(DQPSK) modulation scheme, said method comprising: receiving the DQPSKoptical signal and converting the DQPSK optical signal into an in-phasesignal and a quadrature-phase signal by a reception demodulation unit;multiplexing the in-phase signal and the quadrature-phase signal by amultiplexer and transmitting the resulting signals to a de-serializingunit; converting the multiplexed signals into parallel signals by ade-serializing unit and transmitting the parallel signals to a receptionprocessing unit; comparing, in the reception processing unit, theparallel signals to a comparison pattern to identify a reception state,and performing at least one of logic inversion, one-bit delay, and bitswap in response to a reception state other than the object receptionstate, and in response to a reception state related to thede-serializing timing in the de-serializing unit, and repeating the stepof comparing until the frame synchronization is established.

As an embodiment, the reception processing unit compares a parallelframe synchronization pattern received from the de-serializing unit to areception-state-corresponding comparison pattern to identify a receptionstate, performs at least one of logic inversion, one-bit delay, and bitswap in response to identification results of a reception state otherthan the object reception state, and in response to a reception staterelated to the de-serializing timing in the de-serializing unit, andperforms at least one of logic inversion, one-bit delay, and bit swap inresponse to a reception state related to the de-serializing timing inthe de-serializing unit when the frame synchronization is notestablished, and repeats the steps of comparing and performing until theframe synchronization is established.

According to the present invention, when the reception frame processingunit detects out-of-frame-synchronization (LOF (Loss of Frame) or OOF(Out of Frame)), the controller controls logical inversion operations inthe clock and data recovery, a multiplexing timing in the multiplexer,and controls the delay interferometer in the front end; thereby, it ispossible to perform frame synchronization pull-in operations to attainan object signal reception state.

In addition, by providing a frame synchronization circuit in thereception frame processing unit that includes plural framesynchronization units corresponding to combinations of pluralsynchronization bit strings, it is possible to quickly identify thesignal reception state, and it is possible to perform the framesynchronization pull-in operations quickly to attain the object signalreception state.

In addition, because an in-phase detector is provided to detect whethera quadrature phase relation holds based on exclusive OR logic betweenthe in-phase signal and the quadrature-phase signal input to themultiplexer, and the controller shifts the phase of the delayinterferometers by π/2 or −π/2 based on the result of exclusive OR logicbetween the in-phase signal and the quadrature-phase signal, it ispossible to perform frame synchronization pull-in operations to attainan object signal reception state by controlling logical inversionoperations in the clock and data recovery and the multiplexing timing inthe multiplexer, and by controlling the delay interferometers in thefront end.

According to the present invention, because the front end includes apolarization controller, a delay interferometer, a polarizing beamsplitter, and a differential light receiver, the signal reception deviceincludes only one delay interferometer; hence it is possible to make thesignal reception device compact and simplify control of the signalreception device.

According to the present invention, because an in-phase detector isprovided to detect whether a quadrature phase relation holds based onexclusive OR logic between the in-phase signal and the quadrature-phasesignal input to the multiplexer, and the controller shifts the phase ofthe delay interferometers by π/2 or −π/2 based on the result ofexclusive OR logic between the in-phase signal and the quadrature-phasesignal, it is possible to attain an object signal reception state bycontrolling the delay interferometers in the front end.

According to the present invention, optical signals are received andmodulated to produce an in-phase signal and a quadrature-phase signal,and the in-phase signal and the quadrature-phase signal are multiplexedand transmitted to a de-serializing unit, the multiplexed signals areconverted into parallel signals and transmitted to a receptionprocessing unit.

When performing a reception process of the optical signals, because itcannot be determined which of a reception state 1 and a reception state2 is being processed from a relation between the order of multiplexingthe in-phase signal and the quadrature-phase signal and thede-serializing timing of the multiplexed signals, in the presentinvention, for example, it is determined whether frame synchronizationis possible after identifying a reception state corresponding to thereception state 1, and carrying out logic inversion, one-bit delay, andbit swap; when frame synchronization cannot be established, the logicinversion, one-bit delay, and bit swap are performed assuming the stateis the reception state 2. In this way, it is possible to perform controlto automatically obtain the object reception state corresponding tovarious reception conditions.

These and other objects, features, and advantages of the presentinvention will become more apparent from the following detaileddescription of the preferred embodiments given with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a block diagram illustrating a principal portion of anoptical signal receiver according to a first embodiment of the presentinvention, used in an optical communication system for transmittingDQPSK optical signals;

FIG. 1B is a table illustrating reception states of DQPSK signals in thesignal reception device of the first embodiment;

FIG. 2A and FIG. 2B are diagrams and waveforms explaining the logicalinversion control in the clock and data recovery 3 or 4 according to thefirst embodiment;

FIG. 3A and FIG. 3B are diagrams and waveforms explaining the timingcontrol in the multiplexer (MUX) 6 with a multiplexing ratio of 2:1according to the first embodiment;

FIG. 4 is a block diagram illustrating a principal portion of an opticalsignal receiver according to a second embodiment of the presentinvention;

FIG. 5 is a table corresponding to the table in FIG. 2 showing receptionstates of DQPSK signals, with 16 different combinations of OA1 and OA2being indicated in the second embodiment;

FIG. 6 is a block diagram illustrating a principal portion of an opticalsignal receiver according to a third embodiment of the presentinvention;

FIG. 7 is a flowchart illustrating operations of the OTUk-FAS detectioncircuit 25 in the third embodiment;

FIG. 8A is a block diagram illustrating a principal portion of anoptical signal receiver according to a fourth embodiment of the presentinvention used in an optical communication system for transmitting theDQPSK optical signals;

FIG. 8B is a table illustrating reception states of DQPSK signals in thesignal reception device of the fourth embodiment;

FIG. 9A is a block diagram illustrating a configuration of the in-phasedetection circuit 31 in the fourth embodiment;

FIG. 9B is a table illustrating relations between states of signals“Port A Data”, “Port B Data”, and signals “Output i”, “Output j” fromthe discrimination decision circuits 36, 37 in the fourth embodiment;

FIG. 10A is a block diagram illustrating a principal portion of anoptical signal receiver according to a fifth embodiment of the presentinvention used in an optical communication system for transmitting theDQPSK optical signals;

FIG. 10B is a table illustrating reception states of DQPSK signals inthe signal reception device of the fifth embodiment;

FIG. 11 is a block diagram illustrating a specific configuration of aprincipal portion of the optical signal receiver in the fifthembodiment;

FIG. 12 is a block diagram illustrating a principal portion of anoptical signal receiver according to a sixth embodiment of the presentinvention used in an optical communication system for transmitting theDQPSK optical signals;

FIG. 13A is a block diagram illustrating a principal portion of anoptical signal receiver according to a seventh embodiment of the presentinvention used in an optical communication system for transmitting theDQPSK optical signals;

FIG. 13B is a table illustrating reception states of DQPSK signals inthe signal reception device of the seventh embodiment;

FIG. 14A is a block diagram illustrating an example of the receptionframe processing unit 9 (framer LSI) according to the seventhembodiment;

FIG. 14B is a table illustrating settings of registers in the logicalinversion circuit 53;

FIG. 15 is a block diagram illustrating another example of the receptionframe processing unit 9 (framer LSI) according to the seventhembodiment;

FIG. 16 is a block diagram illustrating still another example of thereception frame processing unit 9 (framer LSI) according to the seventhembodiment;

FIG. 17 is a block diagram illustrating a principal portion of anoptical signal receiver according to an eighth embodiment of the presentinvention used in an optical communication system for transmitting theDQPSK optical signals;

FIG. 18 is a block diagram illustrating an example of the receptionframe processing unit 9 (framer LSI) according to the presentembodiment.

FIG. 19 is a block diagram illustrating another example of the receptionframe processing unit 9 (framer LSI) according to the present embodimenthaving a function of one-bit shift;

FIG. 20 is a block diagram illustrating a principal portion of anoptical signal receiver according to a ninth embodiment of the presentinvention used in an optical communication system for transmitting theDQPSK optical signals;

FIG. 21 is a block diagram illustrating still another example of thereception frame processing unit 9 (framer LSI) according to the ninthembodiment;

FIG. 22 is a block diagram illustrating another example of the receptionframe processing unit 9 (framer LSI) according to the present embodimenthaving a function of one-bit shift;

FIG. 23A is a block diagram illustrating a principal portion of anoptical signal receiver according to a 10th embodiment of the presentinvention used in an optical communication system for transmitting DPSK(Differential Phase Shift Keying) optical signals;

FIG. 23B is a table illustrating a correspondence relation between DPSKsignal reception states and FAS bytes;

FIG. 24A is a block diagram illustrating an example of the receptionframe processing unit 209 (framer LSI) according to the 10th embodiment;

FIG. 24B is a table illustrating settings of registers in the logicalinversion circuit 53;

FIG. 25 is a block diagram illustrating still another example of thereception frame processing unit 209 according to the 10th embodiment;

FIG. 26 is a block diagram illustrating a principal portion of anoptical signal receiver according to an 11th embodiment of the presentinvention used in an optical communication system for transmitting DPSK(Differential Phase Shift Keying) optical signals;

FIG. 27 is a block diagram illustrating a principal portion of anoptical signal receiver according to a 12th embodiment of the presentinvention used in an optical communication system for transmitting DPSK(Differential Phase Shift Keying) optical signals;

FIG. 28 is a block diagram illustrating a principal portion of anoptical signal receiver according to a 13th embodiment of the presentinvention, used in an optical communication system for transmittingDQPSK optical signals;

FIG. 29 is a block diagram illustrating a principal portion of thereception processing unit 9 according to the present embodiment;

FIG. 30 is a table illustrating the reception states and controloperations as described with reference to FIG. 28 and FIG. 29;

FIG. 31 is a flowchart illustrating operations of an optical signalreceiver according to a 14th embodiment of the present invention, whichis used in an optical communication system for transmitting DQPSKoptical signals;

FIG. 32 is a table illustrating reception states and control operationscorresponding to operations shown in FIG. 31;

FIG. 33A through FIG. 33D are tables illustrating reception states of anoptical signal receiver according to a 15th embodiment of the presentinvention, which is used in an optical communication system fortransmitting DQPSK optical signals;

FIG. 34 is a table illustrating reception states and control operationscorresponding to the above-described four states in FIG. 33A throughFIG. 33D;

FIG. 35 is a block diagram illustrating a structure of the principalportion of the reception processing unit 9 according to a 15thembodiment. In FIG. 35, the same reference numbers are assigned to thesame elements as those shown previously;

FIG. 36 is a table illustrating reception states and control operationswhen the phase difference between the π/4 delay interferometer and the−π/4 delay interferometer (as shown in FIG. 28) is maintained to be π/2.

FIG. 37 is a flowchart illustrating operations of the optical signalreceiver according to the 16th embodiment of the present invention,which is used in an optical communication system for transmitting DQPSKoptical signals;

FIG. 38 is a block diagram illustrating an optical transponder (anoptical sender and an optical receiver) employing the IM-DQPSKmodulation scheme in the related art;

FIG. 39 is a circuit diagram illustrating an example of a configurationof a DQPSK precoder in the related art; and

FIG. 40 is a block diagram illustrating a principal portion of anoptical signal receiver used in an optical communication system fortransmitting the DQPSK optical signals in the related art.

DETAILED DESCRIPTION OF EMBODIMENTS

Below, embodiments of the present invention are explained with referenceto the accompanying drawings.

First Embodiment

FIG. 1A is a block diagram illustrating a principal portion of anoptical signal receiver according to a first embodiment of the presentinvention, used in an optical communication system for transmitting theDQPSK optical signals.

The optical signal receiver illustrated in FIG. 1A includes a front end1 that has two delay interferometers and opto-electric conversionelements that receives DQPSK optical signals and converts the DQPSKoptical signals into in-phase signals I and quadrature-phase signals Q;clock and data recovery 3 and 4 that regenerate clock and data signalsbased on the in-phase signals I and the quadrature-phase signals Q; amultiplexer 6 that multiplexes the in-phase signals I and thequadrature-phase signals Q output from the clock and data recoveries 3and 4; a reception frame processing unit 9 that detects framesynchronization based on the signals multiplexed by the multiplexer 6;and a controller 10 that, based on an out-of-frame-synchronizationdetection result (LOF (Loss of Frame) or OOF (Out of Frame)) from thereception frame processing unit 9, controls logical inversion operationsin the clock and data recoveries 3 and 4, or controls a multiplexingtiming in the multiplexer 6, or controls the delay interferometers inthe front end 1.

Specifically, the optical signal receiver illustrated in FIG. 1Aincludes the front end 1 (40 G DQPSK OR) that receives and demodulatesthe DQPSK optical signals, the delay interferometer controller 2, theclock and data recovery (20 G CDR A) 3, the clock and data recovery (20G CDR B) 4, a clock and data recovery controller (CDR controller) 5, themultiplexer (MUX) 6 with a multiplexing ratio of 2:1, a multiplexercontroller 7, a de-serializer (DES) 8, a reception frame processing unit(framer-LSI) 9, and a controller 10.

The reception frame processing unit 9 has the functions of signalreception processing of DQPSK optical signals the same as the framer inthe related art. In addition, the reception frame processing unit 9 atleast has functions of detecting synchronization of received frames anddetecting LOF and OOF. The detected results are sent to the controller10 as indicated by a dashed-line arrow in FIG. 1A.

In FIG. 1A, it is illustrated that the reception frame processing unit 9processes 16-channel parallel data; certainly, the number of channels ofthe parallel data can be reduced to increase operating speed of thecircuit. On the other hand, the number of channels of the parallel datacan also be increased along with an increase of capacity of thetransmission line.

Until the LOF/OOF detection information (indicated by the dashed-linearrow from the reception frame processing unit 9 in FIG. 1A.)disappears, the controller 10 controls a bias voltage or the temperatureof the delay interferometers through the delay interferometer controller2 (this operation is indicated as “interferometer bias control” in FIG.1A with a dashed-line arrow), performs logical inversion operations ondata signals through the clock and data recovery controller 5 (thisoperation is indicated as “logical inversion control” in FIG. 1A with adashed-line arrow), or controls the multiplexing sequence with amultiplexing ratio of 2:1 through the multiplexer controller 7 (thisoperation is indicated as “MUX timing control” in FIG. 1A with adashed-line arrow).

Specifically, (a) the clock and data recovery controller 5 controls thelogical inversion operations in the clock and data recoveries 3 and 4,(b) the multiplexer controller 7 controls multiplexing times of themultiplexer 6, and (c) the delay interferometer controller 2 controlsthe bias voltage or the temperature so as to adjust a π/4 delayinterferometer and a −π/4 delay interferometer of the front end 1 tooperate at optimum operation points. In addition, phase control isperformed to shift the phase by +π/2±n π or −π/2±n π (n is an integer).Here, the delay interferometer controller 2 can perform the abovecontrols by employing any well-known method.

The above control operations (a), (b), and (c) are repeated until theLOF/OOF detection information from the reception frame processing unit 9disappears.

FIG. 1B is a table illustrating reception states of DQPSK signals in thesignal reception device of the first embodiment.

The table in FIG. 1B shows whether signal reception is allowed of alogically inverted state and a logically non-inverting state of thequadrature-phase signal Q and the in-phase signal I from a port A and aport B of the front end 1, respectively.

In the table in FIG. 1B, for example, a double circle indicates anobject DQPSK signal reception state, single circles indicate states ableto be received after logical inversion control, triangles indicatestates able to be received after a combination of a time shift operationand the logical inversion control, and crosses indicates states thatcannot be received directly.

Assume in the object reception state, the quadrature-phase signal Q isfrom the port A of the front end 1, and the in-phase signal I is fromthe port B of the front end 1, and the reception frame processing unit 9performs frame synchronization pull-in operations to approach thisobject reception state.

First, consider the reception states indicated by single circles in thetable in FIG. 1B. In these reception states, the phase of the signalfrom the port A or the phase of the signal from the port B is inverted;thus it is possible to obtain the phase relation of the object receptionstate by the logical inversion control in the clock and data recoveries3 and 4.

Next, consider the reception states indicated by triangles in the table.In these reception states, both the signal from the port A and thesignal from the port B are different from the object reception state,including phase inverted states. In this case, by a combination of atime shift operation and the logical inversion control, it is possibleto obtain the phase relation of the object reception state, in which theframe synchronization can be attained.

Next, consider the reception states indicated by crosses in the table.These reception states correspond to states that cannot be receiveddirectly. However, by repeating the above-mentioned control operations(a), (b), and (c) to adjust the delay interferometers to operate atoptimum operating points, and by the logical inversion control of theregenerated clock signals and the multiplexing timing control, it ispossible to transition to the object reception state.

FIG. 2A and FIG. 2B are diagrams and waveforms explaining the logicalinversion control in the clock and data recovery 3 or 4 according to thepresent embodiment, including a CDR function section and a CDR LSI, asshown in FIG. 2A and FIG. 2B, where FIG. 2A illustrates the usual stateof the clock and data recovery 3 or 4, and FIG. 2B illustrates a logicalinversion state of the clock and data recovery 3 or 4.

In the usual state, a switch sw is set to operate such that data areinput at 21.5 Gbps from the port A or the port B of the front end 1, anda clock signal at 21.5 Gbps and data at 21.5 Gbps are output. In thisstate, when the clock and data recovery controller 5 performs thelogical inversion control, the switch SW is switched to the inversioncircuit “not”; hence, logic of the output data is inverted.

FIG. 3A and FIG. 3B are diagrams and waveforms explaining the timingcontrol in the multiplexer (MUX) 6 with a multiplexing ratio of 2:1according to the present embodiment, where “Data in port A” indicatesdata input to the multiplexer (MUX) 6 from the port A of the front end 1through the clock and data recovery 3 or 4, “Data in port B” indicatesdata input to the multiplexer (MUX) 6 from the port B of the front end 1through the clock and data recovery 3 or 4, the clock signal from theclock and data recovery 3 or 4 is indicated by “Clock”, and themultiplexed data output from the multiplexer 6 are indicated by “Dataout”. Also illustrated in FIG. 3A and FIG. 3B are a phase shifterdenoted by “π” and a switch sw, in addition to the multiplexer (MUX) 6.

When the data from the port A are multiplexed first, and the data fromthe port B are multiplexed later (it is indicated as “port A->port B” inFIG. 3A), the switch sw switches the Clock signal into the multiplexer(MUX) 6, multiplexing is performed by the multiplexer (MUX) 6, and thecorresponding state is shown by the waveforms of the Clock signal, theTrigger signal, the In port A signal, the In port B signal, and Data outsignal. Here, the Trigger signal controls the In port A data signal tobe output as the Data out signal at the rising time of the Clock signal,and controls the In port B data signal to be output as the Data outsignal at the falling time of the Clock signal. Thereby, data “Data out”multiplexed at a ratio of 2:1 are obtained.

When the data from the port B are multiplexed first, and the data fromthe port A are multiplexed later (it is indicated as “port B->port A” inFIG. 3B), the switch SW switches the Clock signal into the side of thephase shifter “π”, and the phase of the Clock signal is invertedcompared to the port A->port B case by a phase shift of 180 degrees.

As a result, the multiplexing sequence of the port A and port B arereversed, and it is possible to control the multiplexed data “Data out”to switch from a sequence of port A->port B to a sequence of portB->port A.

Second Embodiment

FIG. 4 is a block diagram illustrating a principal portion of an opticalsignal receiver according to a second embodiment of the presentinvention; specifically, FIG. 4 illustrates a principal portion of thereception frame processing unit 9 (framer LSI) as shown in FIG. 1A.

As illustrated in FIG. 4, the reception frame processing unit 9 includesa frame processor 21, a frame synchronization circuit 22, and a signalreception state identifier 23 for identifying signal reception states ofDQPSK signals.

In addition, 16 parallel signals each at 2.7 Gbps are input to thereception frame processing unit 9.

The frame synchronization circuit 22 includes 16 frame synchronizersFSC01 through FSC16, which perform frame synchronization detection ondifferent combinations of synchronization bit strings. In an OTN(Optical Transport Network) signal, as recommended by ITU-T G.709, it isknown that a header of a frame is identified by detecting a FrameAlignment Signal (FAS) used for frame synchronization in the overhead ofa frame. When the Frame Alignment Signal is received to be in a mannerof OA1, OA1, OA1, OA2, OA2, OA2 (here, OA1 represents “11110110”, andOA2 represents “00101000”), it is decided that a frame synchronizationstate is attained, and a frame synchronization signal is sent to theframe processor 21.

Because FAS corresponds to the synchronization bytes A1, A2 of theoverhead of a frame in SONET (Synchronous Optical Network) signals orSDH (Synchronous Digital Hierarchy) signals, the above method is alsoapplicable to SONET (Synchronous Optical Network) signals or SDH(Synchronous Digital Hierarchy) signals.

In the frame synchronization using OA1 and OA2 of FAS, the framesynchronization circuit 22 has 16 frame synchronizers FSC01 throughFSC16 corresponding to 16 different combinations of the in-phase signalI and the quadrature-phase signal Q, including logical inversion statesthereof.

The DQPSK signal reception state identifier 23 receives detectionsignals from the 16 frame synchronizers FSC01 through FSC16, identifiesthe signal reception state by using a detection signal from any one ofthe frame synchronizers FSC01 through FSC16, and notifies the controller10 (refer to FIG. 1) of the signal reception state identificationinformation.

The frame processor 21 has the functions of frame synchronizationpull-in operations, frame de-mapping, and transmitting detection resultsof LOF (Loss of Frame) or OOF (Out of Frame) to the controller 10.

FIG. 5 is a table corresponding to the table in FIG. 1B showingreception states of DQPSK signals, with 16 different combinations of OA1and OA2 being indicated.

These 16 different combinations are detected in parallel, respectively,by the 16 frame synchronizers FSC01 through FSC16 in the framesynchronization circuit 22 as shown in FIG. 4. For example, the objectsignal reception state is indicated by the double circle, correspondingto OA1 _(Q1)=“11110110”, and OA2 _(Q1)=“00101000”, and a detectionsignal from the frame synchronizer FSC01 is input to the DQPSK signalreception state identifier 23. The DQPSK signal reception stateidentifier 23 notifies the controller 10 of the information of the framesynchronization state. In this case, the controller 10 is notified thatthe object reception state is present. When the object reception stateis not present, the controller 10 controls the components thereof togenerate the object reception state, or maintains control conditions.

When a detection signal from one of the frame synchronizers FSC02through FSC04 is input to the DQPSK signal reception state identifier23, it is determined that the logical state of either the in-phasesignal I or the quadrature-phase signal Q is inverted relative to theobject signal reception state indicated by the double circle. The DQPSKsignal reception state identifier 23 notifies the controller 10 of theinformation of the reception state. Receiving this information, asillustrated in FIG. 2, the controller 10 may control the clock and datarecoveries 3 and 4 to execute logical inversion so as to generate thein-phase signal I and the quadrature-phase signal Q of the object signalreception state.

When a detection signal from one of the frame synchronizers FSC05through FSC08 is input to the DQPSK signal reception state identifier23, it is determined that the detected reception state corresponds toone of the reception states indicated by triangles in FIG. 1B. The DQPSKsignal reception state identifier 23 notifies the controller 10 of thereception state information. Receiving this information, the controller10 controls the clock and data recoveries 3 and 4 to execute logicalinversion, as illustrated in FIG. 2, and controls the multiplexer 6 toexecute multiplexing timing control to change the multiplexing order, asillustrated in FIG. 3.

When a detection signal from one of the frame synchronizers FSC09through FSC16 is input to the DQPSK signal reception state identifier23, it is determined that the detected reception state corresponds toone of the reception states indicated by the crosses in FIG. 1B. TheDQPSK signal reception state identifier 23 notifies the controller 10 ofthe reception state information. Because the reception states indicatedby the crosses in FIG. 1B correspond to states that cannot be receiveddirectly, the controller 10 may terminate reception processing, orrepeat the control operations (a), (b), and (c) as described in theprevious embodiment.

In the present embodiment, because the frame synchronizers FSC01 throughFSC16 of the reception frame processing unit 9 handle the DQPSK signalreception states in parallel, it is possible to quickly perform theframe synchronization state pull-in step compared to the method ofrepeating the control operations (a), (b), and (c) sequentially, asdescribed in the previous embodiment.

Third Embodiment

FIG. 6 is a block diagram illustrating a principal portion of an opticalsignal receiver according to a third embodiment of the presentinvention; specifically, FIG. 6 illustrates a principal portion of thereception frame processing unit 9 (framer LSI) as shown in FIG. 1A.

As illustrated in FIG. 6, the reception frame processing unit 9 includesa frame processor 21 a, a frame synchronization circuit 22 a, anOTUk-FAS detection circuit 25, and registers 26. The same as FIG. 4, 16parallel signals each at 2.7 Gbps from the de-serializer (DES) 8 areinput to the reception frame processing unit 9.

The frame synchronization circuit 22 a detects predeterminedsynchronization bits to detect frame synchronization, and sends a framesynchronization signal to the frame processor 21.

In OTN (Optical Transport Network) systems, as recommended by ITU-TG.709, Frame Alignment Signal (FAS) bytes are defined as the framesynchronization bits in an overhead section of an OTU signal, and whenthe Frame Alignment Signal is received to be in a manner OA1, OA1, OA1,OA2, OA2, OA2 (here, OA1 represents “11110110”, and OA2 represents“00101000”), it is decided that a frame synchronization state isattained.

Because FAS corresponds to the synchronization bytes A1, A2 of theoverhead of a frame in SONET (Synchronous Optical Network) signals orSDH (Synchronous Digital Hierarchy) signals, in the case of SONETsignals or SDH signals, the OTUk-FAS detection circuit 25 serves as adetection circuit for detecting the synchronization bytes A1, A2 inSONET signals or SDH signals.

The registers 26 retain 16 different combinations of OA1 and OA2 of FASas shown in FIG. 5, corresponding to variations of the reception statesof the in-phase signal I and the quadrature-phase signal Q. Here, it isassumed that the registers 26 can be rewritten without any limitations.

The OTUk-FAS detection circuit 25, serving as a frame synchronizationdetection circuit, reads in the 16 different combinations of FASretained in the registers 26 sequentially, detects which combination ofOA1 and OA2 corresponds to a successful frame synchronization detection,and notifies the controller 10 of the information of the detectedcombination of OA1 and OA2. As described above, the controller 10controls the components thereof to attain the object reception state.

FIG. 7 is a flowchart illustrating operations of the OTUk-FAS detectioncircuit 25.

In step S1, when the frame synchronization circuit 22 a detects an LOF(Loss of Frame) or OOF (Out of Frame) state, the OTUk-FAS detectioncircuit 25 sets an initial value of a register address to be “0”.

In step S2, the OTUk-FAS detection circuit 25 reads in one of the 16combinations of OA1 and OA2 of FAS retained at the register address inthe registers 26.

In step S3, the OTUk-FAS detection circuit 25 compares the thus obtainedregister value to a received OTUk-FAS byte.

If it is determined that the register value is in agreement with thereceived OTUk-FAS byte in step S4, the value of the OTUk-FAS is outputand sent to the controller 10 in step S5.

If it is determined that the register value is not in agreement with thereceived OTUk-FAS byte in step S4, the register address is incrementedby one in step S6, and the routine returns to step S2 to repeat theoperations from step S2 to step S4.

That is, the OTUk-FAS detection circuit 25 reads in the next combinationof OA1 and OA2 of FAS retained at the new register address in theregisters 26, and compares the newly obtained register value to thereceived OTUk-FAS byte. This routine is repeated until the registervalue is in agreement with the received OTUk-FAS byte. When agreement isdetected, the value of the OTUk-FAS is sent to the controller 10.Receiving the OTUk-FAS value, the controller 10 determines the DQPSKsignal reception state as shown in FIG. 1B, and if the object receptionstate is not attained, the controller 10 controls the components thereofto transition to the object reception state.

Fourth Embodiment

FIG. 8A is a block diagram illustrating a principal portion of anoptical signal receiver according to a fourth embodiment of the presentinvention used in an optical communication system for transmitting theDQPSK optical signals.

In the present embodiment, the same reference numbers are assigned tothe same elements as those shown in FIG. 1A.

The optical signal receiver in FIG. 8A further includes an in-phasedetection circuit 31 having an exclusive OR logical circuit EOR and acounter.

FIG. 8B is a table illustrating reception states of DQPSK signals in thesignal reception device of the present embodiment.

As shown in the table in FIG. 8B, the same as the table in FIG. 1B, withsymbols of double circle, single circles, triangles, and crosses, thetable in FIG. 8B shows conditions for logical inversion control and alogical non-inversion control of the quadrature-phase signal Q and thein-phase signal I from the port A and the port B, respectively.

In addition, a reset signal RST generated by the controller 10 in eachframe period or in correspondence to a low frequency clock signal isinput to the counter of the in-phase detection circuit 31 to reset thecounter and to start counting up in-phase detection signals from theexclusive OR logical circuit EOR. The count prior to the next RST signalis indicated by “Data” in FIG. 8A, and the count “Data” is input to thecontroller 10.

The in-phase detection circuit 31 is able to detect the DQPSK signalreception states indicated by crosses in the table in FIG. 8B, namely,the reception states in which both the signal from the port A and thesignal from the port B are the in-phase signal I or the quadrature-phasesignal Q, or logical inversion of the in-phase signal I or thequadrature-phase signal Q.

When the DQPSK signal reception states indicated by crosses aredetected, the controller 10 directs the delay interferometer controller2 to shift the phase of one interferometer in the front end 1 by π/2 or−π/2. Specifically, as described above, phase control is performed toshift the phase by +π/2±n π or −π/2±n π (n is an integer). Then, thecontroller 10 controls the components so that a normal reception stateis obtained after repeatedly executing the aforesaid control operations(a), (b), and (c).

The same as described with reference to FIG. 1A, and FIG. 1B, until theLOF/OOF detection information (indicated by the dashed-line arrow fromthe reception frame processing unit 9 in FIG. 1A.) disappears, thecontroller 10 controls the bias voltage or the temperature of the delayinterferometers through the delay interferometer controller 2 (indicatedas “interferometer bias control”), performs logical inversion operationson data signals through the clock and data recovery controller 5(indicated as “logical inversion control”), or controls the multiplexingsequence with a multiplexing ratio of 2:1 through the multiplexercontroller 7 (indicated as “MUX timing control”). Further, the in-phasedetection circuit 31 having an exclusive OR logical circuit EOR and acounter performs in-phase detection and notifies the controller 10 ofthe results (this operation is indicated as “in-phase detection” in FIG.8A with a dashed-line arrow).

FIG. 9A is a block diagram illustrating a configuration of the in-phasedetection circuit 31 in the present embodiment.

As illustrated in FIG. 9A, the in-phase detection circuit 31 includes anexclusive OR logical circuit (EOR) 32, an inversion circuit (NOT) 33,counters 34, 35, and discrimination decision circuits 36, 37.

Signals from the port A and the port B of the front end 1 at 21.5 Gbps(indicated by “Port A data” and “Port B data”, respectively) are inputto the exclusive OR logical circuit 32 via the clock and data recoveries3 and 4.

The controller 10 outputs a reset signal RST in each frame period or incorrespondence to a low frequency clock signal. The reset signal RSTresets the counters 34, 35. Output signals from the exclusive OR logicalcircuit EOR are input to the counter 34, and input to the counter 35 viathe inversion circuit 33. The counters 34, 35 count up the input signalsaccording to the clock signal “Clock”.

The counts obtained by the counters 34 and 35 in each preset interval,such as a frame period, are input to the discrimination decisioncircuits 36, 37, and are compared to a reference value. Theidentification circuit 36 and 37 output signals indicating comparisonresults. Specifically, the identification circuit 36 or theidentification circuit 37 outputs a signal at a high level (H) if thecount is greater than the reference value, and outputs a signal at a lowlevel (L) if the count is less than or equal to the reference value. Theoutput signals from the discrimination decision circuits 36, 37 areindicated by “Output i”, “Output j”, respectively in FIG. 9A.

The discrimination decision circuits 36, 37 output the signals “Outputi” and “Output j” to the controller 10.

FIG. 9B is a table illustrating relations between states of signals“Port A Data”, “Port B Data”, and levels (H or L) of signals “Output i”,“Output j” from the discrimination decision circuits 36, 37.

As illustrated in FIG. 9B, when the signal “Port A Data” and the signal“Port B Data” have the same phase, the output signals from the exclusiveOR logical circuit 32 are at the low level (L), whereas when the signal“Port A Data” and the signal “Port B Data” have different phases, theoutput signals from the exclusive OR logical circuit 32 are at the highlevel (H).

Because the counters 34, 35 are configured to count up a high levelsignal at the timing of the clock signal “Clock”, when the input signalsto the counters 34, 35 have the same phase, it turns out that one of thecounters, for example, the counter 34, has a count close to zero, andthe other one of the counters, for example, the counter 35 has a countclose to a maximum. To the contrary, when the input signals to thecounters 34, 35 have different phases, one of the counters, for example,the counter 34, has a count close to the maximum, and the other one ofthe counters, for example, the counter 35 has a count close to zero.Hence, if the output signal “Output i” from the identification circuit36 is at the low level L, and the output signal “Output j” from theidentification circuit 37 is at the high level H, it can be determinedthat the two input signals have the same phase. On the other hand, ifthe output signal “Output i” from the identification circuit 36 and theoutput signal “Output j” from the identification circuit 37 are both atthe high level H or at the low level L, it can be determined that thephase relation between the two input signals is random, that is, thephase relation is undetermined.

Fifth Embodiment

FIG. 10A is a block diagram illustrating a principal portion of anoptical signal receiver according to a fifth embodiment of the presentinvention used in an optical communication system for transmitting theDQPSK optical signals.

In the present embodiment, the same reference numbers are assigned tothe same elements as those shown in FIG. 1A.

As illustrated in FIG. 10A, the front end 1 includes an autopolarization controller APC, a delay interferometer, a polarizing beamsplitter PBS, and opto-electrical conversion elements.

The auto polarization controller APC generates a polarized opticalsignal with a polarization plane at 45 degrees, a polarizationmaintaining fiber transmits the optical signal while maintaining such apolarization plane, and then the polarized optical signal is input tothe delay interferometer.

FIG. 10B is a table illustrating reception states of DQPSK signals inthe signal reception device of the present embodiment.

As illustrated in FIG. 10B, because of the front end 1 as shown in FIG.10A, DQPSK signal reception states indicated by a double circle, asingle circle, and triangles are generated, but other states are notgenerated. That is, there are only four possible combinations thatgenerate logic states.

Then, according to the reception state detection information indicatedby the dashed-line arrow from the reception frame processing unit 9 tothe controller 10, the controller 10 controls the bias voltage or thetemperature of the delay interferometer through the delay interferometercontroller 2 (indicated as “interferometer bias control”), performslogical inversion operations on data signals through the clock and datarecovery controller 5 (indicated as “logical inversion control”), orcontrols the multiplexing sequence with a multiplexing ratio of 2:1through the multiplexer controller 7 (indicated as “MUX timingcontrol”).

FIG. 11 is a block diagram illustrating a specific configuration of aprincipal portion of the optical signal receiver in the presentembodiment.

Shown in FIG. 11 are the front end 1, the clock and data recoveries 3,4, the reception frame processing unit 9, and an optical phase controlcircuit 47 having functions of the delay interferometer controller 2 andthe controller 10.

As illustrated in FIG. 11, the front end 1 includes an auto polarizationcontroller (APC) 41, a polarization maintaining fiber 42, an opticalwave circuit 43, differential light receiving circuits 45, 46, each ofwhich has a pair of opto-electric conversion elements, a delayinterferometer 51, an input-side optical coupler 51 a, arms 51 b, 51 c,an output-side optical coupler 51 d, and polarizing beam splitters (PBS)52, 53.

The auto polarization controller 41 is configured to be able to change apolarization state of a DQPSK optical signal arbitrarily.

The auto polarization controller 41 monitors and automatically controlsthe polarization state of the DQPSK optical signal inside so as togenerate a linearly-polarized light beam having a polarization planeinclined by 45 degrees relative to a birefringence axis of the lower arm51 c below the delay interferometer 51.

The delay interferometer 51 may be a Mach-Zehnder light guide includingthe input-side optical coupler 51 a serving as a branching portion, theupper arm 51 b, the lower arm 51 c, and the output-side optical coupler51 d serving as a combining portion. Optical path lengths of the twoarms 51 b and 51 c are designed to be different from each other so as togenerate a relative time delay τ equivalent to one symbol of the QOPSKoptical signal between light beams propagating through the arms 51 b and51 c.

For example, by setting the total length of the upper arm 51 b longerthan that of the lower arm 51 c, the time delay τ is induced whichdepends on the length of the delay line but is independent of thepolarization state.

In addition, the arm 51 c below the delay interferometer 51 has across-sectional structure different from other components, or theadditives in the substrate of the arm 51 c are different from othercomponents. Due to this, the arm 51 c operates as a light guide havingbirefringence and functioning as a ¼ wavelength plate (λ/4), and is ableto generate a birefringence difference equaling to π/2 between the TEmode and the TM mode for the corresponding one of the two light beamsbranched to the arm 51 c by the input-side optical coupler 51 a.

The light beams formed by splitting performed by the input-side opticalcoupler 51 a and propagating through the upper arm 51 b and the lowerarm 51 c, respectively, are combined by the output-side optical coupler51 d first, and are then branched (split) again into two complementarysignals. One of the two complementary signals is input to the polarizingbeam splitter 52, and the other one of the two complementary signals isinput to the polarizing beam splitter 53.

Each of the polarizing beam splitters 52, 53 has an optical axisparallel to the birefringence axis of the lower arm 51 c below the delayinterferometer 51, and splits the light beam from the delayinterferometer 51 into a TE mode light beam and a TM mode light beam.

The TE mode light beams split by the polarizing beam splitters 52, 53propagate through respective output light guides extending to the end ofthe substrate of the optical wave circuit 43, and enter into thedifferential light receiving circuits 45 and 46 arranged near the end ofthe output light guides.

Similarly, the TM mode light beams split by the polarizing beamsplitters 52, 53 also propagate through respective output light guidesextending to the end of the substrate of the optical wave circuit 43,and enter into the differential light receiving circuits 45 and 46arranged near the end of the output light guides.

In FIG. 11, the output light guides extending from the polarizing beamsplitters 52, 53 to the differential light receiving circuits 45, 46 arearranged to intersect with each other, but the output light guides mayalso be arranged to involve less cross-talk.

The optical wave circuit 43 is controlled by the optical phase controlcircuit 47, for example, to adjust the temperature of the substrate nearthe light guide or the electrical field near the light guide to performoptical phase control in the optical wave circuit 43.

For example, the TE mode light beams split by the polarizing beamsplitters 52, 53 are input to the pair of light receiving elements inthe differential light receiving circuit 45, which outputs a signal Iobtained by demodulating the in-phase component of the DQPSK opticalsignal.

Meanwhile, the TM mode light beams split by the polarizing beamsplitters 52, 53 are input to the pair of light receiving elements inthe differential light receiving circuit 46, which outputs a signal Qobtained by demodulating the quadrature-phase component of the DQPSKoptical signal.

The signal I and the signal Q from the differential light receivingcircuits 45, 46, respectively, are input to the clock and datarecoveries 3, 4 to regenerate the clock signal.

According to the present embodiment, the auto polarization controller 41of the front end 1 changes a polarization state of the input DQPSKoptical signal into a linearly-polarized light beam, specifically,having a polarization plane inclined by 45 degrees relative to thebirefringence axis; the linearly-polarized light beam propagates throughthe polarization maintaining fiber 42 and is input to the optical wavecircuit 43; and the optical wave circuit 43 splits the inputlinearly-polarized light beam into the in-phase signal I and thequadrature-phase signal Q. In the previous embodiments, the front endhas two delay interferometers. In contrast, in the present embodimentthe optical wave circuit 43 has only one delay interferometer 51. Henceit is possible to make the signal reception device compact and simplifythe structure of the signal reception device.

In addition, because a delay time difference equivalent to one symbol ofthe DQPSK optical signal and independent of the polarization state isgenerated by a light guide formed from a delay line, and at the sametime a phase difference is generated between the TE mode light beam andthe TM mode light beam by the upper arm only, thereby shifting theinterference operation point by exactly π/2, it is not necessary tocontrol the phase difference between the in-phase component and thequadrature-phase component. As a result, as illustrated by the DQPSKsignal reception states in the table in FIG. 10B, it is sufficient todetect four reception states, and perform the logical conversion controland the multiplexing timing control.

Therefore, the frame synchronization circuit 22 illustrated in FIG. 4 inthe reception frame processing unit 9 can be configured to include theframe synchronizer FSC01 for detecting the signal reception stateindicated by the double circle, the frame synchronizer FSC04 fordetecting the signal reception state indicated by the single circle, andthe frame synchronizers FSC05, FSC08 for detecting the signal receptionstate indicated by the triangles. Hence, it is possible to simplify thestructure of the frame synchronization circuit 22.

Sixth Embodiment

FIG. 12 is a block diagram illustrating a principal portion of anoptical signal receiver according to a sixth embodiment of the presentinvention used in an optical communication system for transmitting theDQPSK optical signals.

In the present embodiment, the same reference numbers are assigned tothe same elements as those shown in FIG. 1A.

The optical signal receiver in FIG. 12 further includes a clock recovery51, and a clock regeneration controller 52.

For example, as illustrated in FIG. 38, when a phase-modulated opticalsignal is intensity-modulated by an intensity modulator in accordancewith a clock signal to transmit an IM-DQPSK optical signal, the receivedmodulated optical signal is split by an optical coupler 50, and thesplit signals are input to the front end 1 (40 G DQPSK OR) and the clockrecovery 51, respectively. The clock recovery 51 regenerates the clocksignal CLK from the intensity-modulated received optical signalincluding a clock signal component, and regenerated clock signal CLK isinput to the multiplexer 6 (MUX 2:1).

The front end 1, the multiplexer 6, the de-serializer (DES) 8, and thereception frame processing unit (framer-LSI) 9 have the same structuresand operate in the same way as those described in the previousembodiments.

That is, the LOF/OOF detection signal (indicated by a dashed-line arrowfrom the reception frame processing unit 9 in FIG. 12) is input to thecontroller 10, and in order for the LOF/OOF detection signal todisappear, the controller 10 controls the multiplexing sequence in themultiplexer 6 through the multiplexer controller 7 (indicated as “MUXtiming control”), and controls the clock recovery 51 through the clockregeneration controller 52 to perform a logical inversion operation(indicated as “logical inversion control”). As described above withreference to FIG. 2 and FIG. 3, the logical inversion operation isperformed so that the quadrature-phase signal Q and the in-phase signalI attain the object reception state.

In the present embodiment, because only a single clock recovery 51 isprovided instead of the clock and recoveries 3 and 4 in the previousembodiments, which are provided corresponding to the port A and port Bof the front end 1, respectively, it is possible to simplify thestructure of the device.

Seventh Embodiment

FIG. 13A is a block diagram illustrating a principal portion of anoptical signal receiver according to a seventh embodiment of the presentinvention used in an optical communication system for transmitting theDQPSK optical signals.

FIG. 13B is a table illustrating reception states of DQPSK signals inthe signal reception device of the present embodiment.

In the present embodiment, the same reference numbers are assigned tothe same elements as those shown in FIG. 1A and FIG. 4.

The optical signal receiver in FIG. 13A further includes a logicalinversion circuit 53.

The logical inversion circuit 53 has the same function as the logicalinversion control in the clock and data recoveries 3 and 4, as describedwith reference to FIG. 1A and FIG. 2B, to control logical inversion andnon-inversion of the quadrature-phase signal Q and the in-phase signalI.

The logical inversion circuit 53, the frame synchronization circuit 22,and the frame processor 21 are integrated to be a 16-channel parallelprocessing integrated circuit, constituting the reception frameprocessing unit (framer-LSI) 9.

The LOF/OOF detection signal (indicated by a dashed-line arrow from thereception frame processing unit 9 in FIG. 13) is input to the controller10, and in order for the LOF/OOF detection signal to disappear, thecontroller 10 controls the logical inversion circuit 53 via the logicalinversion control indicated by a dashed-line arrow, or controls themultiplexing sequence in the multiplexer (MUX 2:1) 6 through themultiplexer controller 7 by MUX timing control indicated by adashed-line arrow, or controls a bias voltage or the temperature of thedelay interferometer in the front end 1 through the delay interferometercontroller 2 by the interferometer bias control indicated as adashed-line arrow.

FIG. 14A is a block diagram illustrating an example of the receptionframe processing unit 9 (framer LSI) according to the presentembodiment.

FIG. 14B is a table illustrating settings of registers in the logicalinversion circuit 53.

In FIG. 14A, the same reference numbers are assigned to the sameelements as those shown in FIG. 4.

As illustrated in FIG. 14A, the logical inversion circuit 53 processes16-channel parallel input data, thus illustrated as 2.7 G×16 (=43 G).The logical inversion circuit 53 constitutes a 16-channel parallelprocessing circuit from exclusive OR logical circuits EOR01 throughEOR16. In addition, the logical inversion circuit 53 includes registersfor setting the logical inversion control signal from the controller 10(refer to FIG. 13A) to odd-numbered ones and even-numbered ones of theexclusive OR logical circuits EOR01 through EOR16. The exclusive ORlogical circuits EOR01 through EOR16 and the registers constitute anintegrated circuit as the reception frame processing unit (framer-LSI)9.

The odd-numbered exclusive OR logical circuits and the even-numberedexclusive OR logical circuits are configured to independently performlogical inversion control and logical non-inversion control on thequadrature-phase signal Q and the in-phase signal I from the front end1.

For example, the frame processor 21, the frame synchronization circuit22, and the signal reception identifier 23 may have the same structuresas those shown in FIG. 4.

The table in FIG. 14B presents logical relation between the logicalinversion control signal to be set in the registers of the logicalinversion circuit 53, logical inversion of data, and logicalnon-inversion of data, being respectively represented as “registersetting”, “input data”, and “output data”.

As shown in the table in FIG. 14B, when the register setting is 1, thelogical inversion control is performed.

FIG. 15 is a block diagram illustrating another example of the receptionframe processing unit 9 (framer LSI) according to the presentembodiment.

In FIG. 15, the same reference numbers are assigned to the same elementsas those shown in FIG. 14A.

As illustrated in FIG. 15, the logical inversion circuit 53 includeslogic inversion gates (NOT gate) for 16-channel parallel input data,switches SW1 through SW16, switch controllers (indicated as “SW cont.”in FIG. 15) for odd-numbered ones and even-numbered ones of the switchesSW1 through SW16. The exclusive OR logical circuits EOR01 through EOR16and the registers constitute an integrated circuit as the receptionframe processing unit (framer-LSI) 9. The odd-numbered switches and theeven-numbered switches are configured to independently perform logicalinversion control and logical non-inversion control on thequadrature-phase signal Q and the in-phase signal I from the front end1.

FIG. 16 is a block diagram illustrating still another example of thereception frame processing unit 9 (framer LSI) according to the presentembodiment.

In FIG. 16, the same reference numbers are assigned to the same elementsas those shown in FIG. 14A and FIG. 15.

Similar to FIG. 4, in FIG. 16, 16-channel parallel signals each at 2.7Gbps (indicated at 2.7 Gbps×16) from the de-serializer (DES) 8 are inputto the reception frame processing unit 9. The 16-channel parallelsignals are input to the frame synchronization circuit 22 a viaexclusive OR logical circuits EOR01 through EOR16. The exclusive ORlogical circuits EOR01 through EOR16 perform the logical inversioncontrol so that the logical inversion control signal from the controller10 is set in registers corresponding to the odd-numbered ones andeven-numbered ones of the exclusive OR logical circuits EOR01 throughEOR16, and the frame synchronization is established. Here, theodd-numbered exclusive OR logical circuits and the even-numberedexclusive OR logical circuits are configured to independently performlogical inversion control and logical non-inversion control on thequadrature-phase signal Q and the in-phase signal I from the front end1.

As described above, the frame synchronization circuit 22 a is configuredto detect predetermined synchronization bits to perform framesynchronization detection, and supplies a frame synchronizationdetection signal to the frame processor 21 a. For example,

In the OTN (Optical Transport Network) signal, as recommended by ITU-TG.709, the Frame Alignment Signal (FAS) is defined in the overhead of anOTN frame and is used as frame synchronization bits. When OA1(“11110110”) and OA2 (“00101000”) are received in a manner of OA1, OA1,OA1, OA2, OA2, OA2, it is decided that a frame synchronization state isattained, and a frame synchronization signal is sent to the frameprocessor 21 a.

Because FAS corresponds to the synchronization bytes A1, A2 of theoverheads of frames in SONET (Synchronous Optical Network), SDH(Synchronous Digital Hierarchy), in cases of SONET and SDH frames, theOTUk-FAS detection circuit 25 serves as a detection circuit fordetecting the synchronization bytes A1, A2 in SONET signals or SDHsignals.

The registers 26 retain 16 different combinations of OA1 and OA2 of FASas shown in FIG. 5, corresponding to variations of the reception statesof the in-phase signal I and the quadrature-phase signal Q. The OTUk-FASdetection circuit 25, serving as a frame synchronization detectioncircuit, reads in the 16 different combinations of FAS retained in theregisters 26 sequentially, detects which combination of OA1 and OA2corresponds to a successful frame synchronization detection, andnotifies the controller 10 of the information of the detectedcombination of OA1 and OA2. As described above, the controller 10controls the components thereof to attain the object reception state.

Eighth Embodiment

FIG. 17 is a block diagram illustrating a principal portion of anoptical signal receiver according to an eighth embodiment of the presentinvention used in an optical communication system for transmitting theDQPSK optical signals.

In the present embodiment, the same reference numbers are assigned tothe same elements as those shown in FIG. 13.

The optical signal receiver in FIG. 17 further includes a neighboringbit exchanging circuit 54. The neighboring bit exchanging circuit 54,the frame synchronization circuit 22, and the frame processor 21 areintegrated to be an integrated circuit, forming the reception frameprocessing unit (framer-LSI) 9.

The LOF/OOF detection signal (indicated by a dashed-line arrow from thereception frame processing unit 9 in FIG. 17) is input to the controller10, and in order for the LOF/OOF detection signal to disappear, thecontroller 10 controls the neighboring bit exchanging circuit 54, as theMUX timing control indicated by a dashed-line arrow, to exchangeneighboring bits in the 16 channel parallel data, and the controller 10performs the logical inversion and non-inversion control in the clockand data recoveries 3, 4 through the clock and data recovery controller5, as the logical inversion control indicated in FIG. 17 with adashed-line arrow, and controls a bias voltage or the temperature of thedelay interferometer in the front end 1 through the delay interferometercontroller 2, as the interferometer bias control indicated in FIG. 17with a dashed-line arrow.

FIG. 18 is a block diagram illustrating an example of the receptionframe processing unit 9 (framer LSI) according to the presentembodiment.

In FIG. 18, the same reference numbers are assigned to the same elementsas those shown in FIG. 15.

As illustrated in FIG. 18, the neighboring bit exchanging circuit 54includes switches SW for exchanging neighboring bits in the 16 channelparallel data (this is referred to as “bit-swap”), and a switchcontroller (indicated as “SW cont.” in FIG. 18).

A timing control signal from the controller 10 is set in the switchcontroller to control the switching operations of the switches SW.Similar to the switching operations in the multiplexing sequence asdescribed in FIG. 3, the in-phase signal I and the quadrature-phasesignal Q in their object reception states can be input to the frameprocessor 21 and the frame synchronization circuit 22.

The switches SW and the switch controller can be formed by semiconductorelements, and they can be further integrated with the frame processor 21and the frame synchronization circuit 22 to be an integrated circuit toserve as the reception frame processing unit (framer-LSI) 9.

FIG. 19 is a block diagram illustrating another example of the receptionframe processing unit 9 (framer LSI) according to the presentembodiment.

In FIG. 19, the same reference numbers are assigned to the same elementsas those shown in FIG. 18, and overlapping descriptions are omittedappropriately.

As illustrated in FIG. 19, in addition to the components in thereception frame processing unit 9 (framer LSI) shown in FIG. 17 and FIG.18, the reception frame processing unit 9 (framer LSI) shown in FIG. 19further includes a one-bit shifter circuit 55, a controller of theone-bit shifter circuit 55, and a one-bit delay element 56. Thecontroller of the one-bit shifter circuit 55 is indicated as “SEL cont.”in FIG. 19, and the one-bit delay element 56 is indicated as “D” in FIG.19.

The one-bit shifter circuit 55 and the controller thereof are arrangedin front of the neighboring bit exchanging circuit 54 to shift the inputdata by one bit.

The one-bit shifter circuit 55 includes 16 optical selectors, which,indicated by “SEL” in FIG. 19, are connected to the 16 switches SW ofthe neighboring bit exchanging circuit 54.

Ninth Embodiment

FIG. 20 is a block diagram illustrating a principal portion of anoptical signal receiver according to a ninth embodiment of the presentinvention used in an optical communication system for transmitting theDQPSK optical signals.

In the present embodiment, the same reference numbers are assigned tothe same elements as those shown in FIG. 13 and FIG. 17.

The logical inversion circuit 53 and the neighboring bit exchangingcircuit 54 are integrated with the frame processor 21 and the framesynchronization circuit 22 to be an integrated circuit serving as thereception frame processing unit (framer-LSI) 9.

The LOF/OOF detection signal (indicated by a dashed-line arrow from thereception frame processing unit 9 in FIG. 20) is input to the controller10, and in order for the LOF/OOF detection signal to disappear, thecontroller 10 controls the neighboring bit exchanging circuit 54, as theMUX timing control indicated by a dashed-line arrow, controls thelogical inversion circuit 53 to perform the logical inversion control asindicated in FIG. 20 with a dashed-line arrow, and controls a biasvoltage or the temperature of the two delay interferometers in the frontend 1 through the delay interferometer controller 2, as theinterferometer bias control indicated in FIG. 20 with a dashed-linearrow.

FIG. 21 is a block diagram illustrating still another example of thereception frame processing unit 9 (framer LSI) according to the presentembodiment.

The frame processor 21, the frame synchronization circuit 22, thelogical inversion circuit 53 and the neighboring bit exchanging circuit54 are integrated to be a 16-channel parallel processing integratedcircuit.

The logical inversion circuit 53 includes exclusive OR logical circuitsEOR01 through EOR16 and registers. The neighboring bit exchangingcircuit 54 includes switches SW and a switch controller (indicated as“SW cont.” in FIG. 21).

FIG. 22 is a block diagram illustrating another example of the receptionframe processing unit 9 (framer LSI) according to the presentembodiment.

In FIG. 22, the same reference numbers are assigned to the same elementsas those shown in FIG. 21, and overlapping descriptions are omittedappropriately.

As illustrated in FIG. 22, in addition to the components in thereception frame processing unit 9 (framer LSI) shown in FIG. 20 and FIG.21, the reception frame processing unit 9 (framer LSI) shown in FIG. 22further includes a one-bit shifter circuit 55, a controller of theone-bit shifter circuit 55, and a one-bit delay element 56. Thecontroller of the one-bit shifter circuit 55 is indicated as “SEL cont.”in FIG. 22, and the one-bit delay element 56 is indicated as “D” in FIG.22.

The one-bit shifter circuit 55 and the controller thereof are arrangedin front of the neighboring bit exchanging circuit 54 and behind thelogical inversion circuit 53 to shift the data from the logicalinversion circuit 53 by one bit.

The one-bit shifter circuit 55 includes 16 optical selectors, which,indicated by “SEL” in FIG. 22, are connected to the 16 exclusive ORlogical circuits EOR01 through EOR16 of the logical inversion circuit 53and the 16 switches SW of the neighboring bit exchanging circuit 54.

10th Embodiment

FIG. 23A is a block diagram illustrating a principal portion of anoptical signal receiver according to a 10th embodiment of the presentinvention used in an optical communication system for transmitting DPSK(Differential Phase Shift Keying) optical signals.

FIG. 23B is a table illustrating a correspondence relation between DPSKsignal reception states and FAS bytes.

The optical signal receiver illustrated in FIG. 23A includes a front end(DPSK OR) 201 that receives and demodulates DPSK optical signals, aninterferometer controller 202, a clock and data recovery (43 G CDR) 203,a clock and data recovery controller (CDR cont.) 205, a de-serializer(DES) 208, a reception frame processing unit (framer-LSI) 209, acontroller 210, a frame processor 221, a frame synchronization circuit222, and a logical inversion circuit 225.

The table in FIG. 23B illustrates a correspondence relation between DPSKsignal reception states and FAS (Frame Alignment Signal) bytes, and anobject signal reception state is indicated by a double circle.

In the DQPSK modulation scheme, as described above, there are sixteenpossible reception states, while in the DPSK modulation scheme, thereare two possible reception states. For this reason, the logicalinversion circuit 225 is provided to perform logic inversion andnon-inversion operations, and the logical inversion circuit 225, theframe synchronization circuit 222, and the frame processor 221 areintegrated to be an integrated circuit, serving as the reception frameprocessing unit (framer-LSI) 209.

Further, the logical inversion circuit 225, as a separate circuit, maybe provided at an earlier stage of the reception frame processing unit(framer-LSI) 209, which is formed from the frame synchronization circuit222 and the frame processor 221.

A DPSK modulation optical signal at a bit rate of 43 Gbps is input tothe front end 201, and is converted into an electrical signal at a bitrate of 43 Gbps. The electrical signal is input to the clock and datarecovery 203, and the clock and data recovery 203 outputs data at 43Gbps (hence, abbreviated to be “Data 43 G”) and a clock signal at 21.5Gbps (abbreviated to be “CLK 21.5 G”).

The data (Data 43 G and the clock signal (CLK 21.5 G) are input to thede-serializer (DES) 208. The de-serializer (DES) 208 converts the inputsignals to 16 parallel signals each at a bit rate of 2.7 Gbps (2.7G×16), and outputs the 16-channel parallel signals to the receptionframe processing unit 209.

By LOF/OOF detections, the reception frame processing unit 209 notifiesthe controller as indicated by a dashed line in FIG. 23A. In order forthe LOF/OOF detection signal to disappear, the controller 210 controlscomponents of the device. Specifically, the controller 210 controls tohave logical inversion operations performed in the logical inversioncircuit 225 of the reception frame processing unit 209 (this operationis indicated as “logical inversion control” in FIG. 23A with adashed-line arrow) to obtain the object reception state.

In addition, the controller 210 controls a bias voltage or thetemperature of the interferometers through the interferometer controller202 (this operation is indicated as “interferometer bias control” inFIG. 23A with a dashed-line arrow).

FIG. 24A is a block diagram illustrating an example of the receptionframe processing unit 209 (framer LSI) according to the presentembodiment.

FIG. 24B is a table illustrating settings of registers in the logicalinversion circuit 53.

In FIG. 24A, the same reference numbers are assigned to the sameelements as those shown in FIG. 23A.

As illustrated in FIG. 24A, the reception frame processing unit 209 isan integrated circuit including the frame processor 221, the framesynchronization circuit 222, a signal reception state identifier 223,and the logical inversion circuit 225. The logical inversion circuit 225includes exclusive OR logical circuits EOR01 through EOR16, and aregister.

The reception frame processing unit 209 has the same structure as thereception frame processing unit 9 illustrated in FIG. 14A, however, inthe reception frame processing unit 209, the register is shared by theexclusive OR logical circuits EOR01 through EOR16, which are arranged ina manner of 16-channel parallel processing.

The table in FIG. 24B presents a logic relation between the settings inthe registers from the controller 210 and the input data and outputdata. As shown in the table in FIG. 24B, when the register setting is 1,the logical inversion control is performed.

FIG. 25 is a block diagram illustrating still another example of thereception frame processing unit 209 according to the present embodiment.

In FIG. 25, the reception frame processing unit 209 is an integratedcircuit including the frame processor 221, the frame synchronizationcircuit 222 a, an OTUk-FAS detection circuit 222 b, and the logicalinversion circuit 225.

The 16-channel parallel signals each at 2.7 Gbps (indicated at 2.7Gbps×16) from the de-serializer (DES) 208 in FIG. 23A are input to thereception frame processing unit 209.

The frame synchronization circuit 222 a detects predeterminedsynchronization bits to perform frame synchronization detection, andsupplies a frame synchronization detection signal to the frame processor221.

In the OTN (Optical Transport Network) signal, as recommended by ITU-TG.709, Frame Alignment Signal (FAS) is defined in the overhead of an OTNframe and is used as frame synchronization bits. When OA1 (“11110110”)and OA2 (“00101000”) are received in a manner of OA1, OA1, OA1, OA2,OA2, OA2, it is decided that a frame synchronization state is attained,and a frame synchronization signal is sent to the frame processor 221.

Because FAS corresponds to the synchronization bytes A1, A2 of theoverheads of frames in SONET (Synchronous Optical Network), SDH(Synchronous Digital Hierarchy), in cases of SONET, SDH frames, theOTUk-FAS detection circuit 22 b serves as a detection circuit fordetecting the synchronization bytes A1, A2 in SONET signals or SDHsignals.

The registers 226 retain two different combinations of OA1 and OA2 ofFAS which varies depending on the reception states of the DPSKmodulation signal.

Meanwhile, referring to FIG. 6, because the DPQSK modulation scheme isemployed, the registers 26 retain 16 different combinations of OA1 andOA2 of FAS, and the registers 26 can be rewritten without anylimitations.

The OTUk-FAS detection circuit 222 b, serving as a frame synchronizationdetection circuit, reads in the two different combinations of FASretained in the registers 226 sequentially, detects which combination ofOA1 and OA2 corresponds to a successful frame synchronization detection,and notifies the controller 210 of the information of the detectedcombination of OA1 and OA2. As described above, the controller 210controls the components to attain the object reception state.

As shown in FIG. 24A, the logical inversion circuit 225 includesexclusive OR logical circuits EOR01 through EOR16 and a register, andthe controller 210 sets logic inversion and logic non-inversioninformation in the register.

11th Embodiment

FIG. 26 is a block diagram illustrating a principal portion of anoptical signal receiver according to an 11th embodiment of the presentinvention used in an optical communication system for transmitting DPSK(Differential Phase Shift Keying) optical signals.

In FIG. 26, the same reference numbers are assigned to the same elementsas those shown in FIG. 23.

In FIG. 26, the function of the logical inversion circuit 225 in thereception frame processing unit (framer-LSI) 209 shown in FIG. 23A isprovided in the clock and data recovery (43 G CDR) 203.

The LOF/OOF detection signal (indicated by a dashed-line arrow from thereception frame processing unit 209 in FIG. 26) is input to thecontroller 210. In order for the LOF/OOF detection signal to disappear,the controller 210 inputs the logical inversion control signal(indicated as a dashed-line arrow) to the clock and data recovery (43 GCDR) 203 through the clock and data recovery controller (CDR cont.) 205to perform logical inversion operations to obtain the object receptionstate.

In addition, the controller 210 inputs a interferometer bias controlsignal to the front end (DPSK OR) 201 through the interferometercontroller 202 to control the bias voltage or the temperature of theinterferometer of the front end (DPSK OR) 201.

12th Embodiment

FIG. 27 is a block diagram illustrating a principal portion of anoptical signal receiver according to a 12th embodiment of the presentinvention used in an optical communication system for transmitting DPSK(Differential Phase Shift Keying) optical signals.

In FIG. 27, the same reference numbers are assigned to the same elementsas those shown in FIG. 26.

In FIG. 27, the optical signal receiver in includes an optical coupler250, a clock recovery 251, and a clock recovery controller 252.

The clock recovery 251 and the clock regeneration controller 252 havethe same structures and the same functions as those of the clockrecovery 51 and the clock recovery controller 52 in FIG. 12. When aphase-modulated optical signal is intensity-modulated by an intensitymodulator in accordance with a clock signal to transmit an IM-DQPSKoptical signal, the received modulated optical signal is split by theoptical coupler 250, and the split signals are input to the front end201 (40 G DPSK OR) and the clock recovery 251, respectively. The clockrecovery 251 regenerates the clock signal CLK from theintensity-modulated received optical signal including a clock signalcomponent, and the regenerated clock signal CLK is input to thede-serializer (DES) 208.

The front end 201, the de-serializer (DES) 208, and the reception frameprocessing unit (framer-LSI) 209 have the same structures and operate inthe same way as those described in the previous embodiments.

The LOF/OOF detection signal (indicated by a dashed-line arrow from thereception frame processing unit 209 in FIG. 27) is input to thecontroller 210. In order for the LOF/OOF detection signal to disappear,the controller 210 inputs the logical inversion control signal(indicated as a dashed-line arrow) to the clock recovery 251 through theclock recovery controller 252 to performs logical inversion operationsto obtain the object reception state.

In addition, the controller 210 inputs a interferometer bias controlsignal to the front end (DPSK OR) 201 through the interferometercontroller 202 to control the bias voltage or the temperature of theinterferometer of the front end (DPSK OR) 201 to obtain the objectreception state.

13th Embodiment

FIG. 28 is a block diagram illustrating a principal portion of anoptical signal receiver according to a 13th embodiment of the presentinvention, used in an optical communication system for transmittingDQPSK optical signals.

In FIG. 28, the same reference numbers are assigned to the same elementsas those shown previously.

The optical signal receiver illustrated in FIG. 28 includes a receptiondemodulation unit 1 which has plural delay interferometers and pluralopto-electric conversion elements for receiving DQPSK optical signalsand converting each DQPSK optical signal into an in-phase electricalsignal and a quadrature-phase electrical signal, a multiplexer 6 whichmultiplexes the in-phase signal and the quadrature-phase signal, ade-serializing unit (DES) 8 which converts the multiplexed signals fromthe multiplexer 6 into parallel signals, and a reception processing unit9 which receives the parallel signals from the de-serializing unit 8,and performs frame processing including frame synchronizationprocessing. The reception processing unit 9 includes a framesynchronization circuit 9 c for establishing frame synchronization, areception state identification circuit 9 d for identifying receptionstates based on the parallel signals, and a logic processing circuit 9 awhich performs logic inversion, bit delay, and bit swap corresponding tothe reception states other than an object reception state identified bythe reception state identification circuit 9 d, and corresponding to areception state related to a de-serializing timing in the de-serializingunit 8.

In addition, the method of controlling optical signal receptionaccording to the present embodiment includes steps of receiving DQPSKoptical signals and converting each of the DQPSK optical signal into anin-phase signal and a quadrature-phase signal by the receptiondemodulation unit 1, multiplexing the in-phase signal and thequadrature-phase signal by the multiplexer 6 and transmitting theresulting signals to the de-serializing unit 8, converting themultiplexed signals into parallel signals by the de-serializing unit 8and transmitting the parallel signals to the reception processing unit9, and the reception processing unit 9 compares the parallel signals toa comparison pattern to identify a reception state, and performs atleast one of logic inversion, one-bit delay, and bit swap correspondingto reception states other than the object reception state, andcorresponding to a reception state related to the de-serializing timingin the de-serializing unit 8. The above steps are repeated until theframe synchronization is attained.

Specifically, as shown in FIG. 28, the optical signal receiver includesthe reception demodulation unit (indicated as “DQPSK OR”) 1 whichreceives the DQPSK optical signals and demodulates the DQPSK opticalsignals, an interferometer controller 2, clock and data recoveries 3 and4 (indicated as “CDR A, CDR B”), a clock regeneration controller 5(indicated as “CDR cont.”), the multiplexer 6, which is a 2:1multiplexer, a multiplexing controller 7 (indicated as “MUX cont.”), thede-serializing unit (DES: De-Serializer) 8, the reception processingunit 9, the logic processing circuit 9 a, a frame processing unit 9 b,the frame synchronization circuit 9 c, the reception stateidentification circuit 9 d, and a controller 10.

It should be noted that although the DQPSK signal at 40 Gbps is used asan example in the present embodiment, it is certain that the presentembodiment is applicable to DQPSK signals at other transmission rates.

The reception processing unit 9 includes the logic processing circuit 9a, the frame processing unit 9 b, the frame synchronization circuit 9 c,and the reception state identification circuit 9 d, and is able todetect LOF (Loss of Frame or OOF (Out of Frame). The detected results ofLOF/OOF are transmitted to the controller 10 along dashed-line arrow inFIG. 28.

In FIG. 28, it is illustrated that the reception processing unit 9processes 16-channel parallel data; certainly, the number of channels ofthe parallel data can be reduced to increase operating speed of thecircuit. On the other hand, the number of channels of the parallel datacan also be increased along with an increase of capacity of thetransmission line.

Until the LOF/OOF detection information (indicated by the dashed-linearrow from the reception frame processing unit 9 in FIG. 28) disappears,the controller 10 controls a bias voltage or the temperature of thedelay interferometers through the delay interferometer controller 2(this operation is indicated as “interferometer bias control” in FIG. 28with a dashed-line arrow), performs logical inversion operations on datasignals through the clock and data recovery controller 5 (this operationis indicated as “logical inversion control” in FIG. 28 with adashed-line arrow), or controls the multiplexing sequence with amultiplexing ratio of 2:1 through the multiplexer controller 7 (thisoperation is indicated as “MUX timing control” in FIG. 1A with adashed-line arrow).

Specifically, (a) the clock and data recovery controller 5 controls thelogical inversion operations in the clock and data recoveries 3 and 4,(b) the multiplexer controller 7 controls multiplexing timings of themultiplexer 6, and (c) the delay interferometer controller 2 controlsthe bias voltage or the temperature so as to adjust a π/4 delayinterferometer and a −π/4 delay interferometer of the DQPSK receptiondemodulation unit 1 to operate at optimum operation points. In addition,phase control is performed to shift the phase by +π/2±n π or −π/2±n π (nis an integer). Here, the delay interferometer controller 2 can performthe above controls by employing any well-known method.

The above control operations (a), (b), and (c) are repeated until theLOF/OOF detection information from the reception processing unit 9disappears.

Refer to the table in FIG. 33A, which illustrates reception states ofthe DQPSK signals, considering the quadrature-phase signal Qk and thein-phase signal Ik from a channel A (Ach) and a channel B (Bch) of thereception demodulation unit 1, for example, a double circle indicates anobject DQPSK signal reception state, single circles indicate states ableto be received after logical inversion, triangles indicate states ableto be received after a combination of bit swap and the logicalinversion, diamonds indicate states able to be received after bit swap,and crosses indicates states that cannot be received directly. Thereception state identification circuit 9 d of the reception processingunit 9 identifies these reception states, and when the object receptionstate indicated by the double circle is identified, the framesynchronization circuit 9 c of the reception processing unit 9 is ableto perform frame synchronization pull-in. In this case, the controller10 does not control components of the optical signal receiver.

When the reception states indicated by single circles in the table inFIG. 33A is identified, since the phase of the signal from the A channelor the phase of the signal from the B channel is inverted, in these thereception states, the frame synchronization circuit 9 c of the receptionprocessing unit 9 is able to perform frame synchronization pull-in.Hence, the controller 10 controls the clock and data recoveries 3 and 4through the clock regeneration controller 5 to carry out logicalinversion to return to the phase relation of the object reception state.

When the reception states indicated by triangles are identified, sincethese reception states are in a logical inversion state and in a bitswap state, it is possible to obtain the phase relation of the objectreception state by performing both logical inversion control and bitswap.

When the reception states indicated by diamonds are identified, sincethese reception states are in a bit swap state, it is possible to obtainthe phase relation of the object reception state by performing bit swap.

Next, when the reception states indicated by crosses are identified,frame synchronization pull-in cannot be performed at all. However, byrepeating the above-mentioned control operations (a), (b), and (c), thecontroller 10, through the interferometer controller 2, can adjust thedelay interferometers to operate at optimum operating points, and thecontroller 10 can control components of the optical signal receiver toobtain the object reception state. By these controls, the objectreception state can be obtained, and the reception and demodulation ofthe DQPSK signals can be performed.

In the reception states indicated by crosses, at least control of thedelay interferometer of the reception demodulation unit 1 is performed.When the π/4 delay interferometer and the −π/4 delay interferometer areoperated such that the phase difference between the π/4 delayinterferometer and the −π/4 delay interferometer is maintained to beπ/2, the reception state cannot be the reception states indicated bycrosses, thus, control during operations is easy.

Logic inversion in reception states other than the object receptionstate indicated by the double circle may be carried out by controllingthe clock and data recoveries 3 and 4, but it can also be carried out inthe logic processing circuit 9 a of the reception processing unit 9. Inaddition, the logic processing circuit 9 a can be configured to carryout bit swap and one-bit delay.

FIG. 29 is a block diagram illustrating a principal portion of thereception processing unit 9 according to the present embodiment.

In FIG. 29, the same reference numbers are assigned to the same elementsas those shown previously.

As illustrated in FIG. 29, the reception processing unit 9 includes alogical inversion circuit 321, a one-bit delay circuit 322, a bit swapcircuit 323, a frame processor 324, a frame synchronization circuit 325,a DQPSK signal reception state identification circuit 326, and acontroller 327.

The logical inversion circuit 321 includes exclusive OR logical circuitsEOR01 through EOR16, a register “odd ch.” for setting an odd numberchannel, and a register “Even ch.” for setting an even number channel.The one-bit delay circuit 322 includes selectors SEL, a selectorcontroller “SEL cont.”, a delay circuit “D” “delay” for delaying onebit. The bit swap circuit 323 includes switching circuits SW, and aswitching controller “SW cont.”.

The logical inversion circuit 321, the one-bit delay circuit 322, andthe bit swap circuit 323 correspond to the logic processing circuit 9 aas shown in FIG. 28, and the de-serializing unit 8 outputs demodulatedsignals, which include 16 parallel in-phase signals and quadrature-phasesignals (indicated by “2.7 G×16”), to the reception processing unit 9,and these signals are input to the frame processor 324, the framesynchronization circuit 325, and the DQPSK signal reception stateidentification circuit 326 through the logical inversion circuit 321,the one-bit delay circuit 322, and the bit swap circuit 323.

In the frame synchronization circuit 325, for example, in OTN (OpticalTransport Network) systems, as recommended by ITU-T G.709, FrameAlignment Signal (FAS) bytes are defined as the frame synchronizationbits in an overhead section of an OTU signal, and when the FrameAlignment Signal is received to be in a manner of OA1, OA1, OA1, OA2,OA2, OA2 (here, OA1 represents “11110110”, and OA2 represents“00101000”), it is decided that a frame synchronization state isattained.

Because FAS corresponds to the synchronization bytes A1, A2 of theoverhead of a frame in SONET (Synchronous Optical Network) signals orSDH (Synchronous Digital Hierarchy) signals, in the case of SONETsignals or SDH signals, the frame synchronization circuit 325 based onOTUk-FAS detection serves as a detection circuit for detecting thesynchronization bytes A1, A2 in SONET signals or SDH signals.

The DQPSK signal reception state identification circuit 326 receives the16 parallel signals input to the frame synchronization circuit 325, andidentifies the reception state according to the setting of the OTUk-FAScomparison byte from the controller 327. Alternatively, when the framesynchronization circuit 325 is configured to detect framesynchronization by parallel processing in 16 channels, it is possible toidentify the reception state based on the detection results of the 16channels, respectively. The DQPSK signal reception state identificationcircuit 326 notifies the controller 327 of identified information of thesignal reception state. The controller 327 may be provided in thecontroller 10 as shown in FIG. 28 to control the components of theoptical signal receiver based on the information of the signal receptionstate.

The controller 327 performs setting of logic inversion, one-bit delay,and bit swap according to notification of reception states from theDQPSK signal reception state identification circuit 326. For example, iflogic “1” is set in the odd channel setting unit “odd ch.”, logicinversion is allowed by the odd-numbered exclusive OR logical circuits.When one-bit delay is performed, the selector SEL is controlled by theselector controller “SEL cont.” of the one-bit delay circuit 322, andafter the signal serial sequence prior to conversion to 16 parallelsignals is delayed by one bit, the signal serial sequence is convertedinto 16 parallel signals. Thus, the output signals of the exclusive ORlogical circuits EOR01 through EOR16 become output signals EOR02 throughEOR16, and EOR01, and are input to the bit swap circuit 323. At thismoment, by the one-bit circuit D, the output signal of the exclusive ORlogical circuit EOR16 is delayed by one bit, and is output to the outputof the exclusive OR logical circuit EOR1.

The bit swap circuit 323 exchanges neighboring bits of the 16 paralleldata. The bit swap circuit 323 performs controls equivalent to thatcontrolling bit arrangement order by controlling multiplexing timing ofthe multiplexer 6 in FIG. 28, therefore, in a structure having the bitswap circuit 323, the multiplexing timing controller as shown in FIG. 28can be omitted.

FIG. 30 is a table illustrating the reception states and controloperations as described with reference to FIG. 28 and FIG. 29.

In FIG. 30, “BS” stands for bit swap control, “1D” stands for one bitdelay control, MZI stands for interferometer control, and a checkindicates the corresponding control is conducted. The 16-bit pattern,which is obtained by conversion to 16 channels in the de-serializingunit 8 and is input to the reception processing unit 9, is referred toas “DQPSK comparison pattern”, and there are 16 patterns numbered from 1to 16. For example, with the No. 13 DQPSK comparison pattern “1111 01100010 1000”, if states of the reception state (1) and reception state (2)(refer to FIG. 41 and FIG. 42A through FIG. 42C) are the object DQPSKsignal reception state indicated by the double circle, in the receptionstate (1), the signal sequence of the odd numbered signal and the evennumbered signal consecutively is Ik, Qk, and in the reception state (2),the signal sequence of the odd numbered signal and the even-numberedsignal consecutively is Qk,Ik+1 (please refer to the presentation on thetime axis of the RZ-DQPSK optical signals in FIG. 41). In the case ofthe object DQPSK signal reception state, the frame synchronizationpull-in can be performed, and frame synchronization signals from theframe synchronization circuit 325 can be input to the frame processor324.

As for No. 2, 5, 6, 11, 12, 15, 16 comparison patterns, states of thereception state (1) and reception state (2) are indicated by crosses;since the interferometer control MZI is performed regardless of thereception state (1) or reception state (2), the controller 10 as shownin FIG. 28 controls the bias voltage or the temperature of the delayinterferometers through the delay interferometer controller 2, thereby,the reception state is controlled to approach the state indicated by thetriangle, the diamond, the single circle, and the double circle.

As for No. 3 comparison pattern, states of the reception state (1) andreception state (2) are indicated by triangles. If the reception state(1) is identified, even numbered logic inversion and bit swap BS arecarried out. In this case, the even number channel setting register“Even ch.” of the logical inversion circuit 321 is set to be “1”, andlogic inversion is performed by the exclusive logic OR circuit, and theswitching circuit SW is controlled by the switching controller “SWcont.”, thereby, the odd numbered channel and the even numbered channelare exchanged. If the reception state (2) is identified, odd numberedlogic inversion, bit swap, and one-bit delay are carried out.

As for No. 4 comparison pattern, states of the reception state (1) andreception state (2) are indicated by diamonds. If the reception state(1) is identified, bit swap BS is carried out. If the reception state(2) is identified, bit swap and one-bit delay are carried out.

As for No. 9 comparison pattern, states of the reception state (1) andreception state (2) are indicated by single circles. If the receptionstate (1) is identified, odd numbered logic inversion is carried out. Ifthe reception state (2) is identified, even numbered logic inversion iscarried out.

As described above, by controlling components of the optical signalreceiver of the present embodiment corresponding to the reception state(1) and reception state (2), it is possible to obtain the objectreception state, hence, not only when starting operation of the opticalsignal receiver, but also in the course of operation of the opticalsignal receiver, it is possible determine the reception state even whenvarious conditions change, and it is possible to obtain the objectsignal reception state by corresponding control.

14th Embodiment

FIG. 31 is a flowchart illustrating operations of an optical signalreceiver according to a 14th embodiment of the present invention, whichis used in an optical communication system for transmitting DQPSKoptical signals.

FIG. 32 is a table illustrating reception states and control operationscorresponding to operations shown in FIG. 31.

In the operations shown in FIG. 31, the phase difference between the π/4delay interferometer and the −π/4 delay interferometer (as shown in FIG.28) is maintained to be π/2. In other words, it is not necessary toperform control on the delay interferometers, thus, the reception statesindicated by crosses as shown in FIG. 30 can be excluded. Therefore, asshown in FIG. 32, there are only reception states indicated by doublecircles, single circles, triangles, and diamonds, and there are onlyeight types of control operations for the reception state (1) andreception state (2). In the table in FIG. 32, when the DQPSK comparisonpattern is in agreement with “1111 0110 0010 1000”, the object receptionstate (No. 7) indicated by the double circle is obtained.

Refer to the flowchart in FIG. 31, in step A1, a DQPSK comparisonpattern P is initialized. Specifically, as shown by the symbol “P<-1” inFIG. 31, the DQPSK comparison pattern P is set to be the first DQPSKcomparison pattern (1010 1100 0100 0001) in the table in FIG. 32.

In step A2, in this way, the DQPSK comparison pattern Pis setcorresponding to the current order number in the table in FIG. 32.

In step A3, the controller 327, as shown in FIG. 29, sets the OTUk-FAScomparison byte in the DQPSK signal reception state identificationcircuit 326, and determines whether the pattern represented by theOTUk-FAS comparison byte in the DQPSK signal reception stateidentification circuit 326 is in agreement with the current DQPSKcomparison pattern P.

If the pattern is in agreement with the DQPSK comparison pattern P, theroutine proceeds to step A4; if the pattern is not in agreement with theDQPSK comparison pattern P, the routine proceeds to step A6 to set thecurrent DQPSK comparison pattern to be the next DQPSK comparison patternin the table in FIG. 32. Then, the routine proceeds to step A2 to repeatstep A2 and step A3 until the pattern is in agreement with the currentDQPSK comparison pattern.

For example, if the DQPSK comparison pattern P currently equals thefirst DQPSK comparison pattern (1010 1100 0100 0001) in the table inFIG. 32, then after step A6, the DQPSK comparison pattern P becomes thesecond DQPSK comparison pattern (1111 1001 0001 0100) in the table inFIG. 32.

In step A4, if the pattern is in agreement with the DQPSK comparisonpattern P, control of the reception state (1) corresponding to thepattern P is performed. For example, when the pattern is in agreementwith the first DQPSK comparison pattern in the table in FIG. 32, thereception states are indicated by triangles, and since it is predictedthat the control operations on the reception state (1) include logicinversion of even channels and bit swap, the logical inversion circuit321 is controlled to carry out logic inversion of even channels, and thebit swap circuit 323 is controlled to exchange bits of neighboringchannels.

In step A5, it is determined whether OUT (Optical Transport Unit) 3frame synchronization is attained. Specifically, the framesynchronization circuit 325 as shown in FIG. 29 determines whether framesynchronization is attained.

If the frame synchronization is attained, it indicates that the objectreception state is obtained, hence the routine is finished.

If the frame synchronization is not attained, the routine proceeds tostep A7.

In step A6, as shown by the symbol “P<-P+1” in FIG. 31, the DQPSKcomparison pattern P is set to be the next DQPSK comparison pattern inthe table in FIG. 32. Then, the routine proceeds to step A2 to repeatoperations in step A2 and step A3.

In step A7, since the frame synchronization circuit 325 determines thatframe synchronization is not attained after pattern agreementdetermination and control of the reception state (1), control of thereception state (2) corresponding to the pattern P is performed.

In step A8, it is determined whether OUT (Optical Transport Unit) 3frame synchronization is attained.

If the frame synchronization is attained, it indicates that the objectreception state is obtained, hence the routine is finished.

If the frame synchronization is not attained, the routine proceeds tostep A6 to set the DQPSK comparison pattern P to be the next DQPSKcomparison pattern in the table in FIG. 32, and then, repeat operationsin step A2 through step A8.

It should be noted that the order of the DQPSK comparison patterns inthe tables in FIG. 30 and FIG. 32 is just an example, it is certain thatthe DQPSK comparison patterns can be arranged in different order.

In addition, it is described above that the DQPSK comparison patternsare selected sequentially to identify the reception state, but the firstto eighth DQPSK comparison patterns in the tables in FIG. 32 may bestored in the DQPSK signal reception state identification circuit 326 inadvance, and comparison may be made with each of the eight DQPSKcomparison patterns to find the matching DQPSK comparison pattern, andthereby to identify the reception state.

15th Embodiment

FIG. 33A through FIG. 33D are tables illustrating reception states of anoptical signal receiver according to a 15th embodiment of the presentinvention, which is used in an optical communication system fortransmitting DQPSK optical signals.

Specifically, FIG. 33A illustrates reception states when the π/4 delayinterferometer and the −π/4 delay interferometer of the receptionprocessing unit 1 (as shown in FIG. 28) are controlled via thecontroller 10.

As described above, in the table in FIG. 33A, a double circle indicatesan object DQPSK signal reception state, and there are totally 16 typesof reception states indicated respectively by the double circle, singlecircles, triangles, a diamond, and crosses.

If the phase difference between the π/4 delay interferometer and the−π/4 delay interferometer is controlled to be about π/2, the receptionstates indicated by crosses disappear, and there are only four possiblereception states.

FIG. 33B illustrates reception states when the phase difference betweenthe π/4 delay interferometer and the −π/4 delay interferometer iscontrolled to be about π/2.

As shown in FIG. 33B, there are only four possible reception statesindicated by open squares, including one reception state indicated bythe double circle, one reception state indicated by the single circle,and two reception states indicated by the triangles.

In addition, if the phase of multiplexing in the multiplexer 6 (as shownin FIG. 28) is fixed completely, since the header position cannot bedetermined based on the frame synchronization when the de-serializingunit 8 converts the multiplexed signals from the multiplexer 6 into 16parallel signals, as described above, there are the reception state (1)and reception state (2) in the reception processing unit 9. Thus, the 16parallel signals input to the reception processing unit 9 correspond tothe reception state (1) or the reception state (2).

FIG. 33C illustrates the reception states (1).

FIG. 33D illustrates the reception states (2).

As shown in FIG. 33C and FIG. 33D, there are only four possiblereception states indicated by open squares, including one receptionstate indicated by the double circle, one reception state indicated bythe single circle, and two reception states indicated by the triangles.

FIG. 34 is a table illustrating reception states and control operationscorresponding to the above-described four states in FIG. 33A throughFIG. 33D.

By selecting and setting the four types of DQPSK comparison patterns(No. 1 to No. 4) as shown in the table in FIG. 34, it is possible toidentify the reception states, and the logical inversion circuit 321,the one-bit delay circuit 322, and the bit swap circuit 323 (as shown inFIG. 29) are controlled corresponding to the reception states.

For example, the No. 1 item in the table in FIG. 34 corresponds to theNo. 3 item in the table in FIG. 30, the states of the reception state(1) and reception state (2) are indicated by triangles. If the receptionstate (1) is identified, even numbered logic inversion is carried out bythe logical inversion circuit 321, and bit swap is carried out by thebit swap circuit 323. If the reception state (2) is identified, oddnumbered logic inversion is carried out by the logical inversion circuit321, bit swap is carried out by the bit swap circuit 323, and one-bitdelay is carried out by the one-bit delay circuit 322. As a result, theobject reception state indicated by the double circle is obtained.

The No. 3 item in the table in FIG. 34 corresponds to the No. 10 item inthe table in FIG. 30, the states of the reception state (1) andreception state (2) are indicated by single circles. In the receptionstates (1) and (2), odd numbered logic inversion and even numbered logicinversion are carried out by the logical inversion circuit 321,respectively.

In the present embodiment, since it is possible to use four types ofDQPSK comparison patterns, corresponding to one reception stateindicated by the double circle, one reception state indicated by thesingle circle, and two reception states indicated by the triangles, forthe reception state identification, it is sufficient for the DQPSKsignal reception state identification circuit 326 (as shown in FIG. 29)to set four types of DQPSK comparison patterns for parallel comparison,thereby, it is possible to perform the reception state identificationquickly.

15th Embodiment

FIG. 35 is a block diagram illustrating a structure of the principalportion of the reception processing unit 9 according to a 15thembodiment. In FIG. 35, the same reference numbers are assigned to thesame elements as those shown previously.

As illustrated in FIG. 35, the reception processing unit 9 includes alogical inversion circuit 331, a one-bit delay circuit 332, a bit swapcircuit 333, a frame processor 334, a frame synchronization circuit 335,a DQPSK signal reception state identification circuit 336, and acontroller 337.

The logical inversion circuit 331 includes exclusive OR logical circuitsEOR01 through EOR16, a register “Odd ch.” for setting an odd numberchannel, and a register “Even ch.” for setting an even number channel.The one-bit delay circuit 332 includes selectors SEL, a selectorcontroller “SEL cont.”, a delay circuit “D” “delay” for delaying onebit. The bit swap circuit 333 includes switching circuits SW, and aswitching controller “SW cont.”.

The one-bit delay circuit 332 and the bit swap circuit 333 correspond tothe logic processing circuit 9 a as shown in FIG. 28,

The one-bit delay circuit 322, the logical inversion circuit 321, andthe bit swap circuit 323 correspond to the logic processing circuit 9 aas shown in FIG. 28, and the de-serializing unit 8 outputs demodulatedsignals, which include 16 parallel in-phase signals and quadrature-phasesignals (indicated by “2.7 G×16”), to the reception processing unit 9,and these signals are input to the frame processor 334, the framesynchronization circuit 335, and the DQPSK signal reception stateidentification circuit 336 through the one-bit delay circuit 332, thelogical inversion circuit 331, and the bit swap circuit 333.

FIG. 36 is a table illustrating reception states and control operationswhen the phase difference between the π/4 delay interferometer and the−π/4 delay interferometer (as shown in FIG. 28) is maintained to be π/2.As described above, in this case, it is not necessary to perform controlon the delay interferometers, thus, the reception states indicated bycrosses as shown in FIG. 30 can be excluded. Therefore, as shown in FIG.36, there are only reception states indicated by double circles, singlecircles, triangles, and diamonds, and there are only eight types ofcontrol operations for the reception state (1) and reception state (3).In the table in FIG. 36, when the DQPSK comparison pattern is inagreement with “1111 0110 0010 1000”, the object reception state (No. 7)indicated by the double circle is obtained.

For the reception state (1) the same as the reception state (1) in FIG.32, the control operations are the same, for the reception state (3),which correspond to the reception state (2) in FIG. 32. However, asshown in FIG. 35, since the logical inversion circuit 331 is connectedto the output end of the one-bit delay circuit 332, the controloperations are different.

FIG. 37 is a flowchart illustrating operations of the optical signalreceiver according to the 16th embodiment of the present invention,which is used in an optical communication system for transmitting DQPSKoptical signals.

In step B1, a DQPSK comparison pattern P is initialized. Specifically,as shown by the symbol “P<-1” in FIG. 37, the DQPSK comparison pattern Pis set to be the first DQPSK comparison pattern (1010 1100 0100 0001) inthe table in FIG. 36.

In step B2, in this way, the DQPSK comparison pattern P is setcorresponding to the current order number in the table in FIG. 36.

In step B3, the controller 337, as shown in FIG. 35, sets the OTUk-FAScomparison byte in the DQPSK signal reception state identificationcircuit 336, and determines whether the pattern represented by theOTUk-FAS comparison byte in the DQPSK signal reception stateidentification circuit 336 is in agreement with the current DQPSKcomparison pattern P.

If the pattern is in agreement with the DQPSK comparison pattern P, theroutine proceeds to step B4; if the pattern is not in agreement with theDQPSK comparison pattern P, the routine proceeds to step B6 to set thecurrent DQPSK comparison pattern to be the next DQPSK comparison patternin the table in FIG. 36. Then, the routine proceeds to step B2 to repeatstep B2 and step B3 until the pattern is in agreement with the currentDQPSK comparison pattern.

For example, if the DQPSK comparison pattern P currently equals thefirst DQPSK comparison pattern (1010 1100 0100 0001) in the table inFIG. 36, then after step B6, the DQPSK comparison pattern P becomes thesecond DQPSK comparison pattern (1111 1001 0001 0100) in the table inFIG. 36.

In step B4, if the pattern is in agreement with the DQPSK comparisonpattern P, control of the reception state (1) corresponding to thepattern P is performed. For example, when the pattern is in agreementwith the first DQPSK comparison pattern in the table in FIG. 36, thereception states are indicated by triangles, and since it is predictedthat the control operations on the reception state (1) include logicinversion of even channels and bit swap, the logical inversion circuit331 as shown in FIG. 35 is controlled to carry out logic inversion ofeven channels, and the bit swap circuit 333 is controlled to exchangebits of neighboring channels.

In step B5, it is determined whether OUT (Optical Transport Unit) 3frame synchronization is attained. Specifically, the framesynchronization circuit 335 as shown in FIG. 35 determines whether framesynchronization is attained.

If the frame synchronization is attained, it indicates that the objectreception state is obtained, hence the routine is finished.

If the frame synchronization is not attained, the routine proceeds tostep B7.

In step B6, as shown by the symbol “P<-P+1” in FIG. 33, the DQPSKcomparison pattern P is set to be the next DQPSK comparison pattern inthe table in FIG. 36. Then, the routine proceeds to step B2 to repeatoperations in step B2 and step B3.

In step B7, since the frame synchronization circuit 335 determines thatframe synchronization is not attained after pattern agreementdetermination and control of the reception state (1), the one-bit delaycircuit 332 (as shown in FIG. 35) is controlled to perform one-bit delayin addition to control of the reception state (1), and the resultingreception state is regarded as the “reception state (3)” in FIG. 36.

In step B8, it is determined whether OUT (Optical Transport Unit) 3frame synchronization is attained.

If the frame synchronization is attained, it indicates that the objectreception state is obtained, hence the routine is finished.

If the frame synchronization is not attained, the routine proceeds tostep B6 to set the DQPSK comparison pattern P to be the next DQPSKcomparison pattern in the table in FIG. 36, and then, repeat operationsin step B2 through B8.

It should be noted that the order of the DQPSK comparison patterns inthe tables in FIG. 36 is just an example, it is certain that the DQPSKcomparison patterns can be arranged in different order.

In addition, it is described above that the DQPSK comparison patternsare selected sequentially to identify the reception state, but the firstto eighth DQPSK comparison patterns in the tables in FIG. 36 may bestored in the DQPSK signal reception state identification circuit 336 inadvance, and comparison may be made with each of the eight DQPSKcomparison patterns to find the matching DQPSK comparison pattern, andthereby to identify the reception state.

While the invention has been described with reference to specificembodiments chosen for purpose of illustration, it should be apparentthat the invention is not limited to these embodiments, but numerousmodifications could be made thereto by those skilled in the art withoutdeparting from the basic concept and scope of the invention.

This patent application is based on Japanese priority patentapplications No. 2005-054371 filed on Feb. 28, 2005, No. 2005-206467filed on Jul. 15, 2005, and No. 2006-116291 filed on Apr. 20, 2006, theentire contents of which are hereby incorporated by reference.

1. A signal reception device for receiving and demodulating an opticalsignal modulated by a Differential Quadrature Phase Shift Keying (DQPSK)modulation scheme, said signal reception device comprising: a receptiondemodulation unit that includes a plurality of delay interferometers anda plurality of opto-electric conversion elements for receiving the DQPSKoptical signal and converting the DQPSK optical signal into an in-phasesignal and a quadrature-phase signal; a multiplexer that multiplexes thein-phase signal and the quadrature-phase signal; a de-serializing unitthat converts the multiplexed signals from the multiplexer into parallelsignals; and a reception processing unit that receives the parallelsignals from the de-serializing unit, and performs frame processingincluding frame synchronization processing, wherein the receptionprocessing unit includes a frame synchronization circuit thatestablishes frame synchronization, a reception state identificationcircuit that identifies reception states based on the parallel signals,and a logic processing circuit that performs logic inversion, bit delay,and bit swap corresponding to a reception state other than an objectreception state identified by the reception state identificationcircuit, and corresponding to a reception state related to ade-serializing timing in the de-serializing unit.
 2. The signalreception device as claimed in claim 1, wherein the logic processingcircuit of the reception processing unit includes: a logic inversioncircuit that controls, corresponding to a reception state identified bythe reception state identification circuit, whether to perform logicinversion on the received parallel signals from the de-serializing unit,a one-bit delay circuit that has a selector and a delay circuit tocontrol whether or not to delay the received parallel signals by onebit, and a bit swap circuit that has a switching circuit for exchangingbits between adjacent channels of the received parallel signals.
 3. Thesignal reception device as claimed in claim 1, wherein the receptionstate identification circuit compares a parallel frame synchronizationpattern received from the de-serializing unit to areception-state-corresponding comparison pattern to identify a receptionstate, and the reception processing unit further includes a controllerthat controls at least one of the logic inversion circuit, the one-bitdelay circuit, and the bit swap circuit in response to identificationresults of a reception state other than the object reception state givenby the reception state identification circuit, and controls at least oneof the logic inversion circuit, the one-bit delay circuit, and the bitswap circuit in response to a reception state related to thede-serializing timing in the de-serializing unit when the framesynchronization is not established by the frame synchronization circuit.4. The signal reception device as claimed in claim 1, wherein thereception demodulation unit includes a π/4 delay interferometer and a−π/4 delay interferometer, the reception state identification circuit ofthe reception processing unit has four reception-state-correspondingcomparison patterns so as to maintain a phase difference of the π/4delay interferometer and the −π/4 delay interferometer to be π/2, saidfour reception-state-corresponding comparison patterns including theobject reception state, and the reception processing unit furtherincludes a controller that controls at least one of the logic inversioncircuit, the one-bit delay circuit, and the bit swap circuit accordingto a reception state identified by comparing a parallel framesynchronization pattern received from the de-serializing unit to thefour reception-state-corresponding comparison patterns, and controls atleast one of the logic inversion circuit, the one-bit delay circuit, andthe bit swap circuit in response to a reception state related to thede-serializing timing in the de-serializing unit when the framesynchronization is not established by the frame synchronization circuit.5. A method of controlling signal reception for receiving anddemodulating an optical signal modulated by a Differential QuadraturePhase Shift Keying (DQPSK) modulation scheme, said method comprising:receiving the DQPSK optical signal and converting the DQPSK opticalsignal into an in-phase signal and a quadrature-phase signal by areception demodulation unit; multiplexing the in-phase signal and thequadrature-phase signal by a multiplexer and transmitting the resultingsignals to a de-serializing unit; converting the multiplexed signalsinto parallel signals by the de-serializing unit and transmitting theparallel signals to a reception processing unit; comparing, in thereception processing unit, the parallel signals to a comparison patternto identify a reception state, and performing at least one of logicinversion, one-bit delay, and bit swap in response to a reception stateother than the object reception state, and in response to a receptionstate related to the de-serializing timing in the de-serializing unit,and repeating the comparing until the frame synchronization isestablished.
 6. The method as claimed in claim 5, wherein the receptionprocessing unit compares a parallel frame synchronization patternreceived from the de-serializing unit to a reception-state-correspondingcomparison pattern to identify a reception state, performs at least oneof logic inversion, one-bit delay, and bit swap in response toidentification results of a reception state other than the objectreception state, and in response to a reception state related to thede-serializing timing in the de-serializing unit, and performs at leastone of logic inversion, one-bit delay, and bit swap in response to areception state related to the de-serializing timing in thede-serializing unit when the frame synchronization is not established,and repeats comparing and performing until the frame synchronization isestablished.